Endless Game

""If you're playing this game to win you're doing it wrong.""

A computer game that is impossible to "win". You just keep going and going until you are killed. The best you can hope for is a place on the High Scores screen. This was actually the standard before completable games were developed and migrated from PCs to home consoles.

In arcade games, this is a fairly obvious design choice. Once someone "beats" the game, they'll stop putting quarters into it, won't they?

Some of these are technically winnable, but when you win, you are then returned to the start, whereupon you continue playing. Many have an unintentional Kill Screen, which are often a mark of honor to get to, but still ultimately result in death.

If there are enemies to destroy, don't expect any boss fight, since there can only be a limited number of bosses, and these games never end.

Contrast Unwinnable, where the game is supposed to be winnable in the first place (but is not, either because of bugs or because the player made an irreversible mistake).

If the game "loops," but does have an ending or some sort of closure, it's a case of Hard Mode Filler. If the gameplay gradually gets faster and faster to keep the player on their toes, that's Difficulty by Acceleration.

Compare certain Wide Open Sandbox games, where there are simply no winning conditions and the player can continue as long as he or she likes.

Note that this trope applies to most golden age arcade games because of the need for the game to be over in order for other people to play. However, specific examples follow:

Live-Action TV

 * In Star Trek: The Next Generation, the game Strategema could turn into one if neither side can gain a winning advantage. Data uses this fact in order to defeat a person who beat him in a normal version of the game.

Tabletop Games

 * Dungeons & Dragons: Most editions of the game allow the characters to continue playing, if not endlessly at least far longer than any group could ever hope to maintain. In 3rd edition, the rules scaled infinitely (though balance becomes an issue, combats take longer, and adventures are harder and harder to prepare so in practice most DM's draw the game to a close and start over.) The point of the game is the experience and working your way through a shared adventure.
 * While all editions encouraged a beginning, middle, and end to their games, 4th edition is the first to avert this within the game mechanics. When the characters reach 30th level, they achieve their "Epic Destiny." This could be anything from ascending to minor god status, to fading into the shadows becoming a mover and shaker unseen. But the point is you won, you pick up a new sheet and start again.
 * The Dragonlance campaign averted this earlier, with only a few exceptional characters in Krynn above level 18, and none above level 20.
 * The old "colored box" games also had a definitive ending—characters who become immortal, rise to become rulers of the universe, give it up to become mortal again, become immortal again and rise to become rulers of the universe again are recruited into the Old Ones. Um, yay?

Theatre

 * Referenced in Ernest Cline's monologue "When I Was A Kid": "...and there were no multiple levels, there was just one screen... forever. And it just kept getting faster and harder until you died. Just like life."

Action Adventure

 * Critical Mass. The four factions are locked in an unwinnable war, so your character keeps doing missions until he is killed.

Action Game

 * Bubble Trouble, a 1990s game for the Mac. If you pass level 50, it constantly presents random levels as levels 51+ until you run out of lives.
 * Survival mode (arguably the "proper" game mode) in the PC game Crimsonland has the player character being endlessly assaulted from all sides by zombies, aliens, giant spiders, and more. There literally is no way to win.
 * In the arcade game based on the movie Indiana Jones and the Temple of Doom, after crossing the rope bridge, you end up in the "Challenge Round," a kind of eternal bonus room where you have to find the sacred statue. When you finally lay hand on the golden statue, you only get a lump of bonus points and the statue continuously reappears at another random location for some more bonus points. You just go around the level like this ad infinitum.
 * Legend of Kage. You've saved the princess, only to have her captured again, and you get booted back to the start, where the season has changed and the difficulty has increased. Repeat until the machine inevitably wins. It's unlikely you'll even finish one loop of the game, as The Computer Is a Cheating Bastard.
 * The NES version, however, averts it, as there are about 3 to 4 bosses to face after each time you saved the princess, and then it's REALLY over.
 * However...
 * The North Pole and Moon levels in Mr. Driller W (easy and hard, respectively).
 * Pac-Man and its sequels, thought once you've seen all the cut-scenes, you've seen all the "story" has to offer. You might count a "win" as reaching level 256, where the game barfs all over the place and overwrites half the stage with garbage data, destroying the dots over there and making the level impossible to clear. You're still only getting out by losing all your lives, however.
 * I'M GONNA BEAT PACMAN!
 * Qix.
 * Robot Unicorn Attack. "You will fail. Persistence is futile."
 * Solomon's Keep will allow the player to go through "Gauntlet" mode if they finish the game on Demigod difficulty without using Kid Mode. Gauntlet difficulty is similar to Demigod, except that death is now permanent, and if you beat it, you go through it again and again until you die.
 * Burger Time just keeps looping through the same stages, and the enemies eventually get ridiculously fast. Averted in Super BurgerTime, which ends after World 5.

Adventure Game

 * The hard mode of Brad the Game, unlockable by finishing the regular game.

Beat'Em Up

 * Kung-Fu Master for the arcade and NES ends the fifth level with Thomas and Sylvia reunited, only to be told that "their happiness does not continue long," implying that Sylvia just gets kidnapped again. The game then restarts.
 * While the arcade version of Renegade plays this straight, the NES version averts it. Oddly enough, the arcade version actually has something resembling an ending, with Mr. K reuniting with his girlfriend after the fourth stage, while the NES version simply skips to the end credits (the Japanese version of both games had endings).

Driving Game

 * Bump N Jump (arcade): after level 8, levels 4-8 loop indefinitely.
 * Spy Hunter (the original).
 * Zone races in the Wipeout series. Your speed increases slowly and gradually, and the only way out is to crash.
 * Subverted with the arcade driving game S.T.U.N. Runner's Ultimate Challenge. It is supposed to be completely unwinnable, mainly because it serves as one of the high-score boards, but it is possible to make it past all 132793 feet of track. The factory default best distance? 65184 feet - less than half the distance of the course. The game actually has a handler for this exceedingly rare possibility to prevent a crash, which includes a specific sample not heard anywhere else in the game.
 * Atari's APB deserves a special mention because virtually nobody ever knew that it was endless. The ultimate objective was to arrest 15 dangerous criminals, each of which looked different and drove a different vehicle. The levels got harder as you went, and you could continue for as long as your tokens held out. It looked for all the world that if you played long enough, there would eventually be a triumphant victory screen, or at least an acknowledgement of your prowess before the game looped. Nope and nope.
 * In Antarctic Adventure, it's no surprise that the game repeats after 10 stages, since the game's between-stage display shows how the path loops around Antarctica. However, the sequel Penguin Adventure had Multiple Endings.

Edutainment Game

 * Word Munchers, Number Munchers. and Fraction Munchers. On Level 19, the troggles move faster. Nobody has lasted long enough to see if the same thing happens on Level 37.
 * Legend goes that people have lasted past level 100.

Fighting Game

 * Endless Melee/Brawl from Super Smash Bros..
 * Same with Cruel Melee/Brawl, in freakin Spades!
 * Yie Ar Kung-Fu repeats its ten stages endlessly, with no discernible shift in difficulty unless player fatigue counts.
 * Survival Mode in the Tekken games. Each time you win a fight, you gain a little bit of your health back and move on to the next round, which is a little bit harder than the last. Lather, rinse, repeat, until you are inevitably defeated.
 * By extension, most fighters include a Survival Mode.
 * Soul Calibur 2's Conquest Mode in the arcade version. You pick one of four armies, you help them conquer the world, 8 rounds at a time. Once all the enemies are out of the way, the world is yours! And then what happens? A civil war breaks out and splits the victorious army into four factions! Always.

First-Person Shooter

 * Call of Duty: World at War's Nazi Zombies mode. If you manage to get past ten waves, the bloody tally in the corner switches to a number in a simple sans-serif font. It's rumored that the game does eventually end (in a crash!) once you hit an for rounds e.g. 128, 256, 65536, and so on.
 * The April 2009 update for Left 4 Dead added Survival Mode, which is Exactly What It Doesn't Say On The Tin.
 * Halo: Reach's Playable Epilogue. The objective is to "survive"(as long as possible). As Noble Six takes damage, his visor is progressively cracked and dinged, and the HUD indicators start to fail. When damaged enough, the game switches to a cutscene where he discards the helmet and a squad of Elites delivers the coup de grace, shown from the helmet cam's perspective.

4X

 * Sword of the Stars has Progression Wars, in which you keep on jumping galaxies trying to survive an enemy that gets more and more difficult.
 * Civilization has victory conditions, but continues on endlessly if you decide to play just ... one ... more ... turn ...
 * Civilization Revolution avoids this by giving specific winning conditions that, even if you feel the need to specifically avoid them, some one will eventually accomplish, no matter how long it takes.
 * Technically, most versions of Civilization have an ending year, with the game ending (and victory awarded to the highest-scoring civilization) if nobody has beaten the game by that point.

Miscellaneous Games

 * Many of the games on Action 52 loop around to the first level upon "completion" while keeping track of your score. Most of the others, infamously, crash a few levels in. Only a few have a clearly-defined ending.
 * Ooze crashes on level 3 of the more common version of the cartridge, but does have an actual ending on the rarer second version (wonder if anyone actually entered this contest).
 * Mario Paint's fly-swatter game.
 * The third Luna Game does this, after a fashion. After a certain point, the only way to progress forward is to allow yourself to fall into a pit . If you avoid the pits, the forest just goes on forever, simply offering pit after pit to fall into.
 * Tutankham loops after 16 stages, most of which are Hard Mode Filler.

MMORPGs

 * Most MMORPGs could be said to fall into the trope, but especially the greatest MMO of all time, Progress Quest!
 * RuneScape plays with this trope. When all skill levels are maxed out and released quests are completed (which takes years), a message appears: "You have completed the game! GO OUTSIDE! ~Love, Jagex"
 * A number of flash games on Neopets follow this, but scoring well on the high-score tables nets you a permanent trophy. One game, called Neverending Boss Battle, somewhat lampshades this fact by stating outright that you have no chance to actually win.

Platform Game

 * Lampshaded by a Playstation 3 commercial featuring a "completionist" asking Kevin Butler about what to do when finished playing LittleBigPlanet. As advertised, due to the absurdly vast stream of Downloadable Content, you are physically incapable of finishing the game.
 * Donkey Kong, for the most part, though it's notable as being the first game with a true storyline with an ending, even if viewing it doesn't end the game. There appears to be an ending when you manage to save Pauline from the titular ape, but when that's done the game just restarts at a higher difficulty level (and in the American arcade version, with extra levels) so that you can further increase your score until you run out of lives. At iteration 22 (which very very few people have reached), an overflow occurs which causes the time bonus, which is also a death timer, to start at a mere 400, which is far from enough to complete the level. This is the so-called "kill screen".
 * Canabalt.
 * Chuckie Egg.
 * The Arcade mode of ColourFire, in the vein of classic arcade games, only ends when the player dies; enemies just get stronger and spawn more quickly as time goes on. The latter has a limit, but the former doesn't.
 * Lode Runner, particularly Hang On mode in the 25th Anniversary Xbox Live Arcade release.
 * Mega Man 9 and Mega Man 10's Endless Attack.
 * Game Mods have made similar stages for Mega Man 2, Mega Man 3, Mega Man 4, and Mega Man 5.
 * The original Super Mario Bros., and the actual Kobayashi Mario: level -1, the Minus World.
 * In Wario Ware, the first time you play a character's stage, you win once you beat the first boss microgame. After that, it just continues on endlessly, getting faster and more difficult, until you lose all your lives, so all you can do is aim for the high score. Of course, there are rewards for getting a high enough score...
 * Every game in Nintendo's Game & Watch line of LCD handhelds from the 80s falls into this. While some later games like Donkey Kong and Zelda have definite endings, they just repeat a little faster until you run out of lives.

Puzzle Game

 * Dr. Mario. Depending, of course, on the mode.
 * Pipe Dream. Although, sometimes a level would be impossible to win, because the start was surrounded by blocks.
 * Tetris (certain modes).
 * It has actually been shown that, assuming the version of Tetris in question has a (reasonably) unbiased RNG, the endless mode of the game cannot be played "forever." The right sequence of S- and Z-shaped blocks forces the player to leave a hole in one corner, then the opposite corner, and so on; this is an infinite sequence, so if the probability distribution is truly uniform, the probability of hitting it eventually is 1. Official Tetris games' random number generators thus follow a specific algorithm that prevents such unlikely events from ever occurring.
 * The odds of your next piece being the first in the so-called "kill sequence" are about one in "more than the number of atoms in the universe" against. So while it is eventually going to kill you, the universe's heat death is more likely to occur.
 * Completing B-Type mode of Tetris for Game Boy at level 9 and height 5 would show various Nintendo characters dancing to "Trepak" from The Nutcracker, followed by a Buran shuttle launch.
 * In Justin Taylor's short story "Tetris" (in the collection Everything Here Is the Best Thing Ever, the answer is the end of the universe. (Or at least the world.)
 * "Kill sequence" aside, the original NES Tetris becomes impossible without slow motion at Level 29, due to the increased speed making it impossible to get a piece to the extreme left or right of the column and the comparatively slow auto-repeat for the left and right keys common in Tetris games of the day. But people playing in extreme slow-mo can continue: http://www.youtube.com/watch?v=76DAwK3cL9w
 * Tetris TGM 3 Shirase, however, proves otherwise. The game is incredibly fast, but it has a relatively fair randomizer, and a few players can still complete all 13 sections.
 * Versions with "infinite spin" (which prevents a piece from locking into place when the rotate buttons are hit quickly) can be played nigh-infinitely assuming the player has the focus to keep using the technique.
 * And with the right version of Tetris, and no increase in drop speed, it's possible to play forever.
 * A Complete History Of The Soviet Union Through The Eyes Of A Humble Worker, Arranged To The Melody Of Tetris, by Pig With The Face Of A Boy, uses this as a metaphor for how even through a hundred years and two revolutions, things never seems to get any better for the Russians.
 * In Tetris DS, it's technically possible to keep playing forever in endless mode... but after level 99/999 lines, it stops increasing counting your lines or increasing your score, making continuing to play pretty pointless.
 * Meteos becomes this if no opponents are added to a game. It also has a mode called "Deluge" that is this exactly, complete with a high-score screen.
 * Columns, much like the aforementioned Tetris.
 * The survival mode of Critical Mass.
 * Slydris, in both the Survival and Infinite modes. You keep going until you hit the top of the screen and die.

Real Time Strategy

 * This is the final Protoss level of StarCraft II: Wings of Liberty in a nutshell. To get the bonus achievement you have to hold on long enough against Hybrid-led Zerg for the Protoss archive building to finish recording the sum knowledge of Protoss civilization, after which it buries itself in the ground and becomes indestructible. After that, your objective is simply to fight until every last warrior at your disposal is dead.

Roguelike

 * Dwarf Fortress has absolutely no win parameters; you simply play until your fortress dies out for whatever reason, or the action grinds to a standstill because your computer's processing power can't keep up with the ever-increasing number of dwarfs/cats/water/magma/etc, or you get bored, or...
 * Losing is fun, afterall.
 * Same for adventure. You have no way to win, so the best you can hope for is to get a character that will be firmly placed in history as the slaughterer of many figures. Aside from that you really cannot do much to "win".
 * but a continent wide genocide might be attempted.

Role-Playing Game

 * Shadowkeep for the PC was an interesting variation: you could win the game and defeat the Shadow King. HOWEVER, once you did, the game wouldn't end. You had to actually quit the game to end it—and get chided for being a coward and a knave.

Shoot Em Ups

 * A great many vertical scrolling Shoot Em Ups do this, including Tiger Heli, Truxton, Terra Cresta, Fire Shark etc.
 * Even moreso if you count shooters that loop back to the first stage with increased difficulty, such as the Gradius series.
 * The arcade version of Commando, while having more unique levels than the NES version, infinitely repeats after level eight, while the NES version, with only 4 unique stages, ends after the fourth loop, with a Blind Idiot Translation A Winner Is You screen.
 * Crystal Quest theoretically has an ending after level 256, at which point it asks for your name and then sends you back to wave 1 with no points. However, the game is so Nintendo Hard that no one has actually beaten the original game.
 * Geometry Wars, in all its forms. Running Grid Wars without a graphics card (which means slower performance, which means an easier game) is only good for buying a couple of minutes.
 * Missile Command. The only way to avoid THE END is not to play.
 * The old, good, addictive game Prohibition used the "return to start" variant, with your death timer going faster. If anybody ever managed to survive the second run, please say so.
 * The good part is, some versions stored the High Scores on the game floppy, rather than just in RAM.
 * Space Invaders.
 * Xevious. Absurdly, the tagline for this game (at least in Nintendo's VC description) is, "Are you devious enough to beat Xevious?" Later Xevious games, such as Xevious: Fardraut Saga, Xevious: Fardraut Densetsu, Xevious Arrangement, Solvalou, Xevious 3D/G, Super Xevious: GAMP no Nazo, and Xevious Ressurection, do have endings.
 * Tempest (arcade): if you get past level 98 (which is actually a repeat of level 82), you're stuck on "level 99" until you lose all your lives. (However, if you re-enter the level ? whether by clearing it, or by losing a life ? the shape changes to a random choice from the 16 shapes available.)
 * Twin Cobra arcade version: After level 10 (which is nearly impossible to get to without credit-feeding, and levels 6-10 are mainly Hard Mode Filler), the game loops back to level 1 with faster bullets and enemies. Averted with the NES and Genesis versions.
 * Tyrian has two examples:
 * Two other bonus games available in story mode are endless. One occurs at the end of episode 1 and the other is one of the two that can show up at the end of episode 4.
 * The bonus Easter Egg game, Destruct (which is a homage to Scorched Earth, but played in real-time), pits you against the computer on an endless series of random landscapes. The game ends when you decide to quit.
 * The Bullet Hell shooter Warning Forever consists of boss fight after boss fight, with each new boss adapting to what defeated it in the last round, until you run out of lives.
 * It seems like they have a set progression right up until that weak spot you hit last time now has shields and extra turrets on it...
 * Warblade is very definitely this.
 * Levels are arranged into sets of four: The first two are normal, the third one has Giant Mooks in adition to the normal enemies, and the fourth is either a bonus level(get all the enemies before they leave the screen to get an increasing bonus) or a kamikaze level(enemies fly into the level and then fly out. They fire even more than normal, and give small bonuses).
 * After six of these sets of levels, there will be a boss level. Levels XX 25, XX 50, XX 75, and XX 00 are like this.
 * After four of these 25-level blocks, level 101-200 are the same as levels 1-100 but with the enemy formations flipped horizontally.
 * 201-300 are the same as 1-100 but with a small but noticeable speed increase. 301-400 are the same as 201-300 but flipped horizontally, 401-500 is a bit faster again, and so on and so forth forever. The games at the top of the highscore list have levels in the thousands and scores in the tens of billions. Nobody has gotten anywhere near to 10000 levels, though, so it's unknown what happens when the 4-digit level counter breaks.
 * The NES version of Legendary Wings loops back to the first level with a higher difficulty on completion, but the arcade version displays the standard Game Over screen after the ending text.
 * Survival Mode in Heavy Weapon is like this. The PC version's survival mode ends when you lose a life, while the Xbox 360 remake gives you three lives.
 * The remake also has multiplayer modes Arms Race and War Party, the first of which gives each player three lives, while War Party gives you infinite lives and a respawn timer- the game ends when there are no surviving players on the screen.
 * Bosconian

Simulation Games

 * There are two schools of thought about Animal Crossing series. One side thinks AC is a typical Wide Open Sandbox example: the player can never win but can't lose either. The other side claims aversion, citing hints from the shopkeeper in the opening cut scenes that the player "wins" with a fully paid-off mortgage and a perfect town, and the rest of the game is a Playable Epilogue.
 * Will Wright's SimFoo games.
 * Essentially any game with Will Wright's name attached to it is endless. There are two notable exceptions: in SimCity 2000, covering the entire city with Launch Arcologies would make them, well, launch into space, thus effectively ending the game (no population left). In Spore, the Space Age has a number of different goals, including collecting various medals, finding the treasure at the center of the galaxy, and controlling the entire galaxy. Although all the goals will take an extremely long time to complete, once they are completed, the Space game is essentially over.
 * Urban Legend of Zelda has it that once you reach the year 1,000,000 in SC2K, the sun goes nova and burns up everything, The End.
 * And SimAnt, if you manage to wipe out all opposition in the yard and the house. The homeowners give up and sell the house, abandoning it to the ants. I have witnessed this.
 * However, experimental mode is endless, but also has no objective.
 * The lack of win conditions in SimCity is why Will Wright referred to the program as a "software toy" rather than as a "game". But there is "scenario" mode, in which the player is provided with a city that has a problem, and a time limit after which the city is either fits the "win" condition for the scenario or not.
 * Realistically there was a period of 5ish years where all the various Sim games (and there were an unbelievable amount) had win conditions. Games before and after were all sandboxes though.
 * In Sim City 2000 at least, accomplishing the "win condition" only mean that you don't get thrown out of office and can continue playing indefintely. You don't even get A Winner Is You.
 * In Sim Earth, getting your intelligent species to achieve Exodus (all the world's cities take off in giant city-spaceships, returning your planet to the Evolution phase) counts as a "win", although you can still keep playing and try to raise another species through the Evolution, Civilization, Technology and Exodus stages.
 * Eventually though, the sun will expand into a red giant and then you're really done.
 * Sim Farm also had a win condition, though you could continue to play afterward.
 * Sim Isle had numerous victory conditions, even in the sandbox maps, though figuring out how to achieve them was a headache.
 * The Sims: Bustin' Out (at least the GBA version) actually had an ending sequence if you completed all the missions the game gave you.
 * SimTower has reaching TOWER status (i.e., the one above five stars) as a victory condition of sorts, although again, you can keep playing. At least TOWER status gives you a nice wedding at the cathedral (on the 100th floor) that you can use as a convenient "the game is now over" point.
 * SimCity 2000 - almost subverted in the case of this player (who has lost their video to terms of use violation) who has a massive population, no pollution, no crime, and far more to show for three years' planning and development of this ultimate city.
 * The Sims Medieval has Kingdom Ambitions, but once you beat them you can keep playing in the kingdom, and a free-play mode opens up once you beat the first ambition. It does a better job of pretending not to be an Endless Game than The Sims original, though.
 * Justified in the Intellivision game Space Spartans, in which it's actually part of the plot: "In 480 B.C. a small Spartan force held off Xerxes and the entire Persian army, in the famous Battle of Thermopylae. The Spartans chose to die defending the pass into Greece, to give their allies time to prepare for attack. SPACE SPARTANS reenacts this battle in space, in a heroic adventure that pits you against overwhelming alien odds. You are the elite force. Stop the first alien onslaught and a new alien force appears. Hold the aliens back as long as you can and give your home galaxy time to prepare for attack!"
 * Transport Tycoon, being a simulation game in the SimCity vein, does have an "ending" wherein 100 years after the game begins, your company is given a rating and possibly posted on the high score list. You do get to keep playing after this. In the earlier versions, once you reach the year 2070, the year would repeat; OpenTTD doesn't have this limit.
 * A certain mission in Trauma Center: Under The Knife 2 goes on forever unless you use a special move to end it. Otherwise, you're just racking up points until the patient dies.
 * All the missions in Trauma Center are timed. The ones that aren't don't have patients that die.
 * A staple of the Anno Domini games. There are also scenarios and a campaign.
 * Crazy Bus

Sports Games

 * SkiFree never ends. You just keep skiing until a hyper yeti charges in and swallows you whole. It's possible to evade it by entering Fast Mode with the F key, in which case the course will just loop around. The yeti know neither fear nor defeat, however, and will hound you for the rest of your days.
 * The Punch-Out!! remake for Wii. It doesn't matter how good you are at the game; you WILL lose eventually, resulting in the game's Downer Ending. It's possible to beat "Mac's Last Stand"; but after that, it goes into "Champion" mode, in which any fighter (including Glass Joe) can knock you down with just one punch (a reference to the NES game's "Dream Fight" mode where you fight Mike Tyson/Mr. Dream). It keeps going this way until you mess up. There is no "good" ending. To add injury to insult, the file you were using is listed as "retired" afterwards. You can still access it, but you can only play the game's exhibition mode. The game's career mode can never be played again with that file. You have several save slots, but still.
 * Football Manager: The player character manager will never die. So you can play until you get bored or you die in real life.

Third-Person Shooters

 * The "Dead Man Walking" mode in Max Payne 2.

Tower Defense

 * Many Tower Defense games are designed that they are in the beginning cakewalks, towards the middle challenges, later-on challenges that required foresight to handle, and in conclusion impossible. Usually, games such as these possess a fixed growth rate for the enemy's health per level, and/or towers that stop getting stronger or become too costly to upgrade. Some games avert this loss by having fixed missions or a certain number of levels.
 * Monday Night Combat (a Tower Defense game at its core) features two Endless Blitzes (Blitz being the solo/cooperative mode of the game). Sudden Death Blitz literally had endless waves of robots trying to attack your Money Ball, and you and/or your friends simply held out for as long as you could. But when players displayed strategies that allowed them to hold out for hours (until either boredom or the bad luck of a string of boss waves got you), the creators added a Super Sudden Death Blitz on a specialized map. The rules were the same, but the enemy robots came in much stronger numbers and more strategic patterns and the map was less in your favor.

Turn-Based Strategy

 * The classic computer game Crush Crumble and Chomp. The only way to end the game is to (eventually) get killed by the humans.

Wide Open Sandbox

 * Minecraft is this, although a certain thread on the Minecraft forum would suggest otherwise.
 * Minecraft has an End! As of the official release, it has a new area known as "The End," home of the Enderman and the Enderdragon. If you manage to defeat the Enderdragon, then you get The End credits! You still get to keep playing after that, but it is the canon ending at this point.

Other

 * The Ur Example may be the pre-electronic arcade game pinball. You keep going till you run out of balls (lives) and the only reward for playing well is bragging rights.