Killer App

Short for "killer application", a Killer App is a game - or something not a game that's a category killer - so good that it's considered a must-own if you have the system it's released for, and is in fact a reason in and of itself to buy said system. Sure, you'll buy other games, you'll even enjoy them, but when you lay down the bucks for a new system you do it with the understanding that, eventually, you'll be getting an incredible gaming experience that can't be found on a competitor's console. It's for this reason that as far as game systems, Killer Apps are, almost by definition, console exclusives.

In the personal computer world, the spreadsheet program Visicalc was the Killer App for the Apple II, and caused a lot of people to buy them; doing a spreadsheet by hand could take hours or days and was an error-prone, tedious process involving pencil, calculator and lots of erasing. Visicalc would do the cross-calculations on a 100x100 spreadsheet on an Apple II in a matter of minutes and it was always right. Lotus 1-2-3 and DBASE II were the KillerApps for the PC, because it often gave people tools to analyze data as good or better than the corporate IT department could provide them.

It behooves gaming companies to make sure that at least one Killer App is available for their system at launch or very soon afterward. The lack of a true Killer App is speculated to be the reason why PlayStation 3 sales have been disappointing to this point.

Arguing over which Killer App provides the most bang for its buck is a large part of the Console Wars.

The term originates from outside the gaming world, where Killer App was used, especially during the '90s Internet boom, to describe the mythical invention that everyone in America needed and which would make its developers—and their investors—rich beyond their wildest dreams.

The term can also be used on a more serious context, used to refer to a very fundamental and revolutionary application that once discovered, immediately becomes a "must-have". When the term is applied in this manner, only a very few applications apply, including word processors, spreadsheets, database management programs, email clients, and web browsers.

While most products that attain Killer App status are extremely successful and popular, it should be noted here that "creating a true Killer App" is akin to "writing the Great American Novel": everybody wants to, but nobody has yet created (or is likely to create) the definitive Killer App.

Note that a Killer App is more than just a good game. A game can be good, great, critically acclaimed, even an all-time classic... and still not be a Killer App. (Conversely, not all Killer Apps are great by modern standards; some of them seem quite dated today.) A Killer App is insanely popular in its own time, enough so as to single-handedly drive sales for its system. The examples that follow, then, are not just the games that tropers loved, but rather the games that everyone loved; the ones that made their respective systems.

Compare Star-Making Role (equivalent for actors) and Breakthrough Hit (equivalent for creators).

Atari
 * Space Invaders was a major system mover for the Atari 2600, quadrupling its sales, making it the Ur Example.
 * Atari was counting on both Pac-Man and ET the Extraterrestrial to be killer apps for the 2600, and had each produced in wildly optimistic numbers; in fact, more Pac-Man cartridges were produced then there were Atari consoles, on the assumption that the game would be so popular people would buy consoles just to play it. As it turned out, they were only half-right, as they did help to kill the Atari 2600, and very nearly the entire industry.
 * Star Raiders was a bona fide Killer App for the Atari 8 Bit Computers; many people bought the computer just to play the game.
 * Alien vs. Predator and Tempest 2000 were this for the otherwise ill-fated Jaguar.

Colecovision
 * Coleco's competitive acquisition of the console license for Nintendo's Donkey Kong is the main reason the Colecovision console was a contender in the second generation Console Wars. It is rumored that the company released an intentionally poorly-designed version of the game for the Atari 2600, just to make their own system look even better by comparison.

Nintendo "When this game was first announced, we thought it was going to suck. How wrong we were. How wrong we were."
 * The first Super Mario Bros for the original NES, credited with saving a dying video game industry. Super Mario Bros 3 followed a few years later.
 * Likewise, Super Mario World for the SNES.
 * The SNES also floated high on The Legend of Zelda a Link To T He Past and the port of Street Fighter II, which was packaged with the console. The Donkey Kong Country series also allowed the SNES to remain popular into the 32-bit era, while Sega stumbled with the Sega CD, 32X and Sega Saturn confusion.
 * Initially Super Mario 64 and then Mario Kart 64, Golden Eye 1997, The Legend of Zelda Ocarina of Time and Star FOX 64 for the Nintendo 64. The system became infamous later in its lifespan for releasing one or two Killer Apps a year—along with basically nothing else of note.
 * Super Smash Bros.. Melee is the absolute GameCube killer app, as it's still being played competitively more than ten years after its release, a life of a Fighting Game surpassed only by Marvel vs. Capcom 2 by one year.
 * Super Smash Bros.. Melee, Resident Evil 4, Eternal Darkness and Metroid Prime convinced the hardcore gamers that the Game Cube wasn't a kiddie wasteland, to quote the Top 10 Game Cube games video from Screw Attack...


 * Resident Evil 4 was even released as part of Capcom's initiative to bring five new exclusive games to the Gamecube to support the platform. Unfortunately, one of them (Dead Phoenix) was never released, three of them (Resident Evil 4, Viewtiful Joe, Killer7) were ported to the PlayStation 2, and the only game to remain a Game Cube exclusive (P.N.03) didn't sell any copies and was critically panned.
 * Nintendogs, Brain Age (for older gamers), Mario Kart DS and New Super Mario Bros (for the Nintendo Faithful), and its quirkier casual games in general, for the Nintendo DS.
 * The remake of Final Fantasy III wasn't a system killer app as much as a third party support killer app. The same could be said for the remake of Final Fantasy IV.
 * Grand Theft Auto Chinatown Wars wasn't quite the Killer it was expected to be on the DS, but made a huge impact on the iPhone platform. It's success essentially gave the greenlight for other developers to create Darker and Edgier games for your iPhone or iPod Touch.
 * The Wii is an unusual case in that it has had a dozen or so killer apps, but relatively few quality third party titles. At launch, the general public bought it for Wii Sports. For hardcore gamers, it was The Legend of Zelda: Twilight Princess.
 * 2007 saw Wii Play, which helped ensure that most Wii owners would have multiple controllers, party games like Mario Party 8 and Mario and Sonic at the Olympic Games, and Super Mario Galaxy, the 2nd best selling 3D platformer of all time. Wii Fit, which was released in the West in 2008, was more popular than the PlayStation 3 for a while, but support for the peripheral hardware never caught on.
 * 2008 had Mario Kart Wii and Super Smash Bros Brawl Nintendo's premiere games for multiplayer and the best selling games in the history of their genres. Animal Crossing and Wii Music were likely meant to become Killer Apps, but poor reception amongst the hardcore audience turned these into mere hits.
 * 2009 was another year of multiple killer apps. New Super Mario Bros Wii was the big holiday title, and is often given at least partial credit for the resurrection of platformers on consoles. Wii Sports Resort popularized the Wii Motion Plus, which would be used in other games such as Skyward Sword.
 * Since 2009, Ubisoft's Just Dance games have also become this for the Wii. However, the lack of big releases since late 2009 has been tied to the Wii's relative decline compared to the other 7th generation consoles.
 * Castlevania: Circle of the Moon was considered a Killer App when it was first released for the Game Boy Advance. However, more than anything, the GBA was built on the base of the Updated Rerelease, with just about every quality SNES title ported over for a new generation to open their wallets for.
 * Though it's a Base Breaker game, Pokémon Ruby and Sapphire is considered this. Well, they are Pokémon games after all.
 * The Game Boy's original Killer App was Tetris, but the aging system was revitalized late in its lifespan by another smash hit: Pokémon Red and Blue. The various sequels of the latter have kept the tradition, driving large sales of their native platforms.
 * To put this in better perspective, multiple Pokémon games are among the best-selling Game Boy Advance and DS games. The best selling titles on the Game Boy Advance were Ruby and Sapphire, which sold over 15 million units, FireRed/LeafGreen, which sold over 10 million units, and Emerald, with over 6 million units. Even the Pokémon Mystery Dungeon Rescue Team, a spinoff by a 3rd party which also was sold on the DS as Blue version, was one of the system's top 20 selling titles, beating out games like Kingdom Hearts, Golden Sun, Metroid Fusion, and The Legend of Zelda: The Minish Cap. The series was not quite so dominant on the DS, but this was due to the market's growth outstripping the franchise, not a loss in popularity.
 * Pokémon is currently the second-best selling series in the world, with the Mario series leading by a mere 20 million games sold. After a ten year headstart. It remains to be seen if it will pass its older brother, it's too close to call at this point.
 * Pokémon's most recent installment, Pokémon Black and White, came out only a few days before this entry (9/20/10), and it's already the fastest selling DS game in history.
 * The Legend of Zelda: Ocarina of Time again, this time for the Nintendo 3DS. Within two weeks, it had sold over 600,000 copies, or over 20% of the install base. It raised 3DS sales by over 50% the week it came out, despite not being released in America until the next week.
 * Monster Hunter 3G (at least if you live in Japan).
 * Those last three games were the three best selling games in Japan during 2011, despite only being out for less than two months. Super Mario 3D Land sold over five million copies in just two months worldwide, outselling games like Gears of War 3 and Skyrim on the 360. Mario Kart 7 sold 4.3 million in 5 weeks. Put together, the two Mario games represent a third of 3DS software sold in 2011. Combine those Mario games with Ocarina of Time and Nintendogs + cats, you have over one half of all 3DS software sold through 2011.
 * Kid Icarus: Uprising is the 3DS's newest killer app, and Japanese sales figures already have it marked at over 132,000 copies shipped in its first week, firmly in the number-one spot for that week! Add in the US and European sales figures, and it's certainly large enough to warrant being listed here.

Sega
 * The Sonic the Hedgehog series on the Mega Drive/Sega Genesis, as well as the first Madden NFL game for (U.S.) sports fans. The bloody version of the first Mortal Kombat also was a boon in distinguishing it from the SNES.
 * The Genesis port of the arcade version of Strider was also one of the system's earlier killer apps. In addition, the game holds the distinction of being the first game to be released on an 8-megabit cartridge.
 * When Lunar: The Silver Star was released in Japan, it sold almost as many copies as the Sega CD. That, and Sonic CD, were, if not killer apps, the nearest thing the Sega CD/Mega CD had.
 * Sega's Virtua Fighter was such a huge hit in arcades that its various ports sold more than half of all 32X and Saturn machines in Japan.
 * Virtua Fighter 2 was the killer app for Saturn.
 * Sakura Taisen was the other Saturn killer app in Japan. It, and the second game recorded the biggest sales as a Saturn original title, and was ranked #13 place in the Famitsu's 100 all-time favorite games list, leading the series to become one of Sega's most successful franchises.
 * The Panzer Dragoon series are killer apps for the Saturn, despite the fact that the first was the only one that sold well.
 * NiGHTS Into Dreams served as a primary reason to buy a Sega Saturn. Other games for the system with massive popularity include Dragon Force (absolutely no relation to the thrash metal band of the same name) and Saturn Bomberman (often referred to by reviewers as the best game in it's series).
 * The beyond-the-arcade port of Soulcalibur was THE reason to get a Dreamcast, even though it wasn't enough to move sales of the system. Interestingly, the death of the Sega Dreamcast (and the end of Sega's hardware history) was heralded by EA denying Sega a port of Madden NFL, the same killer app that made their own company what it is today, and wouldn't have done so without the parent company's help. Et Tu, Brute?
 * However, NFL2K was one of the rare sports killer apps, becoming one of the biggest sellers at launch along with another killer app in Sonic Adventure, and garnering enough rave reviews that it instigated a still-strong backlash against Madden once EA won the bid to become the sole manufacturer of NFL games. Although Sega was able to fill the void with that and its equally-well-received NBA counterpart, no EA support did punch a big hole in the DC's third-party support.
 * Another killer app was Shenmue, which had generated considerable hype for the console, even though its huge budget eventually led to it becoming a financial failure despite solid sales.

Playstation
 * Battle Arena Toshinden was hyped as the first Killer App for Sony Playstation, a "Virtua Fighter Killer". It took at first, but the quality of later games overtook it and now it's currently forgotten. The real killer apps ended up being Resident Evil, Tomb Raider, Metal Gear Solid, and especially Final Fantasy VII, and to a lesser extent Crash Bandicoot and Spyro the Dragon for younger players. The system's sheer number of killer apps is the main reason it was able to take the video game throne from Nintendo in the mid-nineties.
 * Square Soft's decision to develop Final Fantasy VII for the PlayStation over the N64 played a huge role in Sony's victory over Nintendo during the 32/64-bit era.
 * The PlayStation 2 received four major Killer Apps in the fall of 2001: Gran Turismo 3 A-Spec, Final Fantasy X, especially Metal Gear Solid 2: Sons of Liberty, and of course Grand Theft Auto III. Coincidentally—or perhaps not—this coincided with release of two of its competitors' consoles, Game Cube and Xbox.
 * Due to the anticipation generated by its pre-release hype, Metal Gear Solid 2: Sons of Liberty is credited for the PlayStation 2's victory over the Dreamcast before the game was even released.
 * The Grand Theft Auto series of games had been Killer Apps for the PlayStation from GTAIII onwards until Microsoft pulled a major coup and convinced Rockstar to make Grand Theft Auto IV a multi-platform release.
 * The PlayStation 3 has gained a large upsurge in sales recently, but its true "killer app" is less a specific game and more to do with Sony lowering the price and replacing their nonsensical Dada Ads with something comprehensible.
 * Lair and Haze were meant to be something of a Killer App, but neither were successful as planned. Uncharted 2 is selling well, but not driving sales enough to make a clear killer app.
 * The Gran Turismo series were killer apps on the PS1 and PS2, but Sony Computer Entertainment's fumbling of the GT5 release may have prevented this status for the PS3.
 * Metal Gear Solid 4: Guns of the Patriots was a fairly important killer app for the PlayStation 3. What's most notable is that Snake's appearance in Super Smash Bros. Brawl, specifically his own stage, has a massive amount of Foreshadowing for this game. Foreshadowing on the killer app of a direct competitor.
 * God of War III, though not hurt by being released at the time the price cut was taking effect.
 * The Uncharted series has been this, but it has never been more apparent than with Uncharted 3: Drake's Deception, which sold 3.8 million copies during the first day of release, something rarely heard of for console exclusive games.

Xbox
 * Halo: Combat Evolved. It single-handedly saved Microsoft from being a mere footnote in the Console Wars.
 * And Halo 2 for the X Box Live multiplayer service.
 * And Halo 3 for the Xbox 360. You may notice a theme here.
 * The Halo franchise also cemented the Xbox as "the FPS console", leading to the FPS "arms race" between Microsoft and Sony that lasted through The Noughties.
 * Gears of War and BioShock (series) were among the first great games for the Xbox 360.
 * Mass Effect and its sequels kept the Xbox afloat when the Halo franchise finally started to run out of steam.
 * Like the Game Boy Advance, Xbox Live Arcade has sold mainly on a stream of solid indie, ranging from Geometry Wars to Shadow Complex.
 * This trope is mostly inverted when it comes to Japan, as they has not taken to either system much like it's competition. So far, the closest the 360 has to a killer app there is a hit game that boosts sales for a week or so then they fall back to just selling a few thousand a week until the next hit game. These "boost" games include Blue Dragon (Akira Toriyama's involvement helped, too), Ace Combat 6, Tales of Vesperia (so it was mainly a Fan Boy issue when the PS3 got a port, not a sales issue), Star Ocean: The Last Hope.
 * For XboxLive in Japan, the Killer App is The Idolmaster, even if it isn't for the 360 itself. On the release of the Xbox 360 version, Microsoft sold over four times as many Microsoft points as they had in the past.
 * To elaborate, THE iDOLM@STER singlehandedly resparked the sales for the XBOX 360 on Japan. The success was so great that in some stores they had to close the doors at early in the morning because they were sold out.

PC/MAC
 * Bungie seems to make killer apps where ever they go. Mac's killer app? The Marathon Trilogy.
 * Half-Life and its sequels are some of the best known PC Killer Apps.
 * Counter-Strike was the killer app for the early 2000's golden age of 'real world' LAN Gaming cafes/centres while at the same time causing them to crash in popularity from 2004 onwards when the sequel Counter Strike Source became the killer app for Steam and home based online multiplayer.
 * Star Wars Rebel Assault was THE killer app for CD-ROM, although some say that the time of CD-ROM had dawned and Rebel Assault was just the first major game...
 * There are two candidates for the cross-platform killer app for CD-ROM drives: The 7th Guest and Myst, both often bundled with the drives people bought in order to play them. Interestingly, unlike many of the other games on the list, they currently have a bit of a Seinfeld Is Unfunny status.
 * Attempts had been made for ages to sell 3D accelerators, and while 3dfx's Voodoo made a good argument, it was Unreal that caused people to pour hundreds of dollars into enough system upgrades to see it rendered through Glide.
 * You mean GLQuake wasn't reason enough? (While it's not the first 3D-accelerated version of Quake, with VQuake for Rendition Verite cards having been released earlier, GLQuake made 3dfx Voodoo Graphics cards sell like hotcakes.)
 * Crysis has been a boon to graphics card manufacturers, as hardcore computer gamers have been working hard to build systems that can render its incredible graphics at full detail, even four years after its release!
 * It was also important because at the time, other developers were either abandoning the PC altogether or making ports that used graphics vastly inferior to that of an Xbox 360 or a PlayStation 3 for no good reason. It's safe to say this game single-handedly saved the platform and jump-started its renaissance.
 * Since Macs have historically had few compatible games, every gamer who owns one is essentially required to get certain games. Some examples are the Marathon Trilogy, and anything made by Blizzard Entertainment.
 * Preemptively, Valve releasing Steam and the Source-based games on Mac (Portal 2 and Left 4 Dead 2 in particular) have caused a huge jump of interest in Mac gaming.
 * The Sims can be credited with kicking off the resurgence of casual gaming of the 2000s (along, of course, with internet games).
 * The Age of Empires series, Age of Empires II was in particular one of the most successful and well crafted PC RTS games of its time, and still maintains a large player and modding community despite being a decade old.
 * The LAMP server (Linux, Apache, MySQL, and PHP) let people build servers using off-the-shelf PC hardware, giving Linux a huge boost in its early days. Along with powering much of the Internet, it quickly became the standard for individually-owned game servers.
 * Windows XP only really started to die off in favour of Windows 7 when Battlefield 3 was announced to be Windows 7/Vista exclusive.

SNK
 * The original Samurai Shodown on the Neo Geo home console.
 * Metal Slug, especially 3.

Genre
 * Pop Cap Games owns the casual genre. Most casual games are tweaked knockoffs of Popcap's efforts, which in turn are pretty much just variations of match-3, spot-the-difference, time-management and various simple luck/skill-based physics minigames. Doesn't matter. Popcap owns the entire genre. There are still entire blocks of people who would never call themselves 'gamers' who are obsessed with Bejeweled.
 * Team Fortress Classic was, for the longest time, THE online shooter. Counter-Strike took over, and the market has since fragmented between WW 2 and futuristic/modern shooters.
 * And now Team Fortress 2 seems to have brought it full circle.
 * Guitar Hero turned Rhythm Games from weird J-Pop things (in the eyes of many) to a major western phenomenon.
 * Though it had less casual-appeal than the above, Dance Dance Revolution pretty much kept the arcade scene afloat single-handedly, and no doubt was an inspiration for the physicality of gaming aspects that would become part of the Wii's appeal.
 * Years later, Just Dance would turn dancing games into a genre in its own right, and incidentally helped Ubisoft become the Wii's biggest supporter outside of Nintendo.
 * Do you like Real Time Strategy games? Then you must have tried two of Blizzard Entertainment's best games: Starcraft and Warcraft III.
 * Or Command & Conquer series. For recent years, Dawn of War series or Company of Heroes also count.
 * Similarly, do you like turn-based 4X? If so, then at least one of the Civilization games is probably in your library.
 * For MMORPGs, World of Warcraft. It's the one everyone's heard of, and it has more subscribers than the next 4 biggest (Ultima Online, Final Fantasy XI, EverQuest and EverQuest 2) put together.
 * And for browser MMORPGs, it's Runescape.
 * Do you like Japanese RPGs? You probably have a Pokémon, Final Fantasy, or Dragon Quest game.
 * In fact, Dragon Quest is such a killer app in Japan that even Salarymen will take a day off and students form the most prodigious schools will cut class just to buy a copy on the day it becomes available for sale.
 * There was (and still may be) a law in Japan regarding when Square-Enix can release Dragon Quest games. Generally speaking, they can do it on a Sunday, when most people don't have to work or go to school.
 * Do you like Western RPGs? You've probably played The Elder Scrolls, series or Baldur's Gate.
 * High fantasy not your thing? Then you've probably got at least one Fallout or Mass Effect game in your library.

Formats
 * The Matrix is widely acknowledged to be the killer app for the DVD format. Every store front had the hallway assault and the rooftop bullet time sequence playing on the screens and so many people bought their first DVD player with a copy of The Matrix that the movie might as well have been bundled with the player. It was the first DVD million-seller.
 * Also a two-in-one of sorts: The PlayStation 2 benefited greatly from having a built-in DVD player.
 * The Blu-Ray format had a similar Killer App: Avatar sold 1.5 million copies on its first day, 6.2 million after three weeks. It's also not surprising that the PlayStation 3 is the most popular Blu-ray player.
 * If you can call an entire industry a Killer App for one product: The force that turned VCRs from neat toys to must-have appliances and also settled the VHS/Betamax format wars? Porn.
 * The Simpsons, Family Guy and Firefly proved the success of the DVD Series Boxsets being both financially lucrative and did not ruin reruns of regular TV. See also Uncancelled
 * The case was proved long before Firefly came along. Babylon 5, for example, made half a billion dollars for Warners several years earlier.
 * Half-Life 2 and Counter Strike Source was responsible for Steam's success today, and the popularity of digital distribution as a whole, though that might have something to do with the games requiring Steam to play.

Other
 * Let's not mince words: Porn is the killer app of EVERY new form of communication, to the point that format wars have been decided based on which one was better for/more accepting of porn. The sole exception might be how porn took up HD-DVD first, which eventually lost out to Blu-Ray. However by the time the war was settled, Sony had made it clear they weren't going to make the same mistake Betamax had.
 * For the Apple II, the killer app wasn't a game at all (though there were an awful lot of those): it was the first electronic spreadsheet, VisiCalc. And for the IBM PC, it was the spreadsheet program Lotus 1-2-3.
 * Spreadsheets seem to get a lot of this: Excel, for example, is pretty much Microsoft Office's Killer App.
 * Spreadsheet programs attract the killer app label because the complex financial and statistical functions they enable are exponentially more difficult—sometimes functionally impossible—without the visual/computational assistance of the spreadsheet. Think about how headache- and eyestrain-inducing a complex spreadsheet is (unless you're into that sort of thing). Then imagine ALL the same information presented in a hard-copy ledger. Killer. App.
 * VisiCalc alone was selling more Apple ][ than all of its games combined, actually, and its need for a screen real estate and RAM was a real driver for the Language Card (which added more memory) and 80-column Card (self-evident), and a real reason why both these upgrades were later officially incorporated into the motherboard design.
 * Almost all of the killer apps for MacOS X are made by Apple. Half of them come with the system.
 * Apple originally made a number of killer apps directly on the original Macintosh's launch—MacPaint, MacDraw, and MacWrite—that have been the gold standard ever since for WIMP GUI image editors, drawing programs and word processors. But it was the first WYSIWYG page layout program, PageMaker, that made desktop publishing possible and guaranteed the Mac's most lucrative niche.
 * You could argue that Apple's OS is the killer app of the Macintosh, and recently, Parallels is a very good killer app for Intel Macs since it basically makes the "you can't play as many games on a Mac" argument obsolete.
 * In America, I Love Lucy, Texaco Star Theater, the Army-McCarthy hearings, and the 1960 Presidential debates were television's Killer Apps. In Britain, the coronation of Queen Elizabeth II was this.
 * Sick as it sounds, you could argue that JFK's assassination was also a killer app. Everyone watched the news, and forget about work happening the next day.
 * The moon landings were this in, of all places, South Africa. When the people of South Africa realized that they were the only people in the Western world who couldn't watch Neil Armstrong take his one small, historic step on the surface of the moon, they pressured their government to end its ban on television programming (which it viewed as a morally corrupting influence). They finally lifted the ban in 1975.
 * Ironically, for Japan, which was still only barely out of the post-war devastation and overwhelmingly poor (it was worse there than in North Korea, actually) it was also the Elizabeth II coronation. People were drawing five-year loans with a ridiculously rip-off rates only to be able to watch it.
 * In Britain, the killer app for colour TV was snooker. The 1969 BBC show Pot Black, which showed a single frame of snooker each week, was made to increase the sales of colour TV sets.
 * The series produced the all-time infamous quote from commentator Ted Lowe: "And for those of you who are watching in black and white, the pink is next to the green".
 * This may be an instance of Beam Me Up, Scotty - when the clip was replayed recently, he said "the pink is by the cushion next to the green" - which is rather more helpful - of course, he could have said similar quotes more than once. (It's arguably also a good way to encourage people to buy colour TVs!)
 * The 1990 Gulf War was proverbially the killer app for 24-hour cable news, specifically CNN. Where national networks had to eventually return to their regularly scheduled programming after Iraqi phone lines were cut off, CNN had previously had a permanent line installed and continued broadcasting round-the-clock.
 * The addition of GPS has been a huge mover for handheld computers. Presumably the medium as a whole is based around the want for calendar and contact programs.
 * Taxi work seems to be the Killer App for hybrid cars. No fuel is consumed idling in dense city traffic or waiting for fares, the battery packs are barely affected by massive mileage and indeed seem to thrive on constantly being in use compared to being parked 22-plus hours a day like most personal cars, and both the financial and environmental cost/benefit ratios increase compared to private use.
 * Buses fall into this as well.
 * The Internet had been around in a form similar to what we use today since at least the early 1980s, but it was NCSA Mosaic, the first web browser, that made the network a must-have for computers.
 * Bittorent is the killer app for consumer internet download speed, download caps, and hard drive capacity.