An Advanced Dungeons and Dragons setting that adds up to D&D in SPACE. It has a small but loyal following. Its origins are actually a good Real Life example of making lemonade when the Pointy-Haired Boss of a gaming company hands her writers lemons; really crafty writers realize that the only difference between "They Just Didn't Care" and "Protection From Editors" is perspective. See "the secret history of Spelljammer" in Jeff Grubb's blog.
The year was 1989. It was a dark time for gaming. Although the influence of The Fundamentalists upon gaming had diminished, the forces of TSR had fallen under the control of Lorraine Williams, who was forcing talented and dedicated writers to turn out reams of crap. One piece of crap she demanded they create was a Standard Sci Fi Setting, believing she could cash in on a trend to squeeze yet more money from innocent gamers.
But the Magnificent writers hit upon a Zany Scheme; though they were denied time to playtest the game, they could cram the poor thing with as much Crazy Awesomeness as they could, as she wasn't paying attention to them. So was born Spelljammer - the most bizarre and wonderful setting ever seen in gaming.
Linking each of then-popular D&D campaign settings together by means of the old Ptolemaic view of the cosmos, the worlds of Greyhawk, Dragonlance, and the Forgotten Realms were (along with thousands of other worlds) stated to be contained in their own "crystal spheres", massive hollow balls large enough to contain a whole solar system. Some were heliocentric systems, sometimes geocentric, and some were flat worlds set upon the backs of great tortoises or other "starbeasts". Or something else entirely. The stars you see from your bedroom window are not other suns - they're actually spots of light (or glowing gems) stuck to the interior of your world's crystal sphere. Unless, of course, you're in a sphere that got giant glowing beetles slowly crawling on its inside surface. It happens, too.
Flying ships, called spelljammers (not to be confused with the Spelljammer, a legendary ship miles in length) traverse wildspace, the void within each sphere, traveling from world to world (which always seem to support life no matter their distance from the sun). The ship picks up an "air envelope" when it leaves the atmosphere, so breathing is limited by the number of crew and the size of the ship, and gravity is always directed toward the deck from both above and below. And outside the crystal spheres (accessible through natural portals or transportation magic), lies the Phlogiston (or "the Flow"), a gaseous, highly incendiary substance that's all the colors of the rainbow and lets your ship travel at warp speed as long as you're in one of its currents.
Spelljammer was utterly preposterous, didn't really care one whit about real-world astronomy or physics, and was completely aware of this. Never taking itself all that seriously, it was one of the few inherently fun games that TSR was permitted to publish in those dark times. I'm just going to list out of context some of the things that you will find in Spelljammer besides a deliciously crazy mish-mash of everything D&D had to offer: Weird Science, Space Pirates, Giant Space Hamsters, Stuffy British Elves (who are of course Better), and Gnomes who think that catapults are a good replacement for staircases. If you're into RPGs and have a strong Willing Suspension of Disbelief, check out some of the old sourcebooks for a fun time - though you'll probably have to settle for a download from DriveThruRPG.com; Williams got her revenge on her disrespectful staff by refusing to publish more than a single run of the books during her tenure at TSR.
A parody setting released by the guys who made Hackmaster, HackJammer, attempted to fit the setting to a well-tested set of rules that made it more playable, but for many it was too little too late.
A 3rd edition remake of the setting appeared in an issue of Dungeon Magazine. While thematically identical to the original Spelljammer (although with its own default campaign setting limited to a single system), it removes the Phlogiston/Crystal Spheres to replace them with the vacuum of space and star systems/galaxies, with the notable difference that suns are also portals the Elemental Plane of Fire with their own atmospheres and natural satellites (apparently magic still outright replaces physics). Additionally, a later issue of Dragon Magazine included 3rd edition versions of popular Spelljammer races. Other than that it was mostly abandoned (no proper products) and left to fans.
Spelljammer was teased for Fourth Edition: It's one of the settings listed as possible to see print, and some Spelljammer content made it into the Manual of the Planes (as a ship to sail the Astral Sea and to use to Plane Shift) and Forgotten Realms Campaign Guide (specifically referring to the crystal spheres and phlogiston), but it never materialized. A Spelljammer makes a cameo in one fifth edition adventure. It was teased further, but the developers admitted they're not going to do it. 5E's current release schedule of "as little as they can release without ownership of Forgotten Realms reverting to Ed Greenwood" makes any official release unlikely.
There's one series of novels (The Cloakmaster Cycle), one short-lived DC comic book series, and one Video Game (Spelljammer: Pirates of Realmspace) using this setting. The dedicated fan portal also tracking usenet groups and keeping mirrors of Spelljammer fan-sites that go down is spelljammer.org.
- All Theories Are True: Phlogiston! Crystal spheres!
- All Cosmologies Are True. Somewhere.
- Exclusively Evil: One of the first major D&D settings to start playing with this, from genocidal elves, to a community of relatively decent illithids, to a non-evil Beholder bartender.
- Artificial Gravity: Technically, gravity "carpets" on small objects were a natural phenomenon.
- Attack of the 50-Foot Whatever: lots of, up to Giant Space Hamsters 
- The Battlestar: Armada (Elven), Mammoth (Ogre) and Tsunami (Humans of Wa) are heavily armed carriers of small crafts.
- Space Fighter: The main limitation on such tactics is the cost of power sources for every warboat, thus Wa churn out rudders of propulsion for Locusts, elven Flitters are built upon starfly wings and goblinoid Blades use relatively cheap lifejammers.
- Bishie Sparkle: The Reigar have this as an inherent part of their physical appearance, to the degree where they have weaponized it.
- Bizarre Alien Biology: Almost anything.
- Even peaceful plants, such as starfly tree - its seeds leave the atmosphere and go Space Sailing until they meet a good icy asteroid. Then a seed roots itself, turns its shell into boiler with steam jets and slowly thrusts the ice boulder it sits on to a warmer orbit where it thaws.
- Boisterous Bruiser: The giffs as a race - big hippo-people with a fetish for shiny uniforms, firearms and showy explosions. Seriously.
- Captain Ersatz: The bionoids are basically mass-produced Guyver units, right down to the chest cannon.
- Colony Drop: Not typically, but still, it's considered a possibility.
Zelva Twogg, Secretary for Wildspace Affairs, New Waterdeep: If we could find some way to tow that old dwarven citadel into orbit around our world, we'd have a fantastic station from which we could open trade to the other worlds in this sphere. We'd probably do best to contact some adventurers to do the work for us.
Skrund the Bald, Undermarshall for Pan-Goblin Affairs, New Trollmoor: If we could find some way to tow that old dwarven citadel so that it was heading right for New Waterdeep, we'd be rid of those damned humans in an eyeblink. We'd probably do best to contact some pirates or monsters to do the work for us.
- Crossover: Spelljammer crosses over with Dragonlance, the Forgotten Realms, Greyhawk, and it can crossover with Planescape, but the two rarely if ever did because they were both ways for adventurers to visit different worlds. The setting has the potential to crossover with Ravenloft even, as it has been noted that the Mists can appear even in Wildspace, but the two have never really crossed over due to Spelljammer being a much goofier setting than Ravenloft.
- Crossover Cosmology: Any imaginable cosmology is likely to be implemented in at least one crystal sphere. Somewhere.
- Death From Above: Averted. A flying weapon platform obviously could have an enormous advantage over groundlings, but spelljammers are clumsier in the atmosphere and thus are sitting ducks for anything that can get them. Spelljammer shock can be caused by any sort of damage and failure to replace the helmsman in free fall before hitting the ground means Total Party Kill. Did we mention helms are expensive?..
- An example from Forgotten Realms is "The Three Greenwings Wars". IEF sent Monarch Mordent to aid the defenders of Myth Drannor. It helped a lot, but as the name implies, emerged in one piece from only two battles. The third time man-o-war descended to have a good shot, one huge winged fiend flew up and began chopping a wing with great axe, simply ignoring most of the stuff elves can quickly hurl at him without harming their own ship. The wing falls off, spelljammer shock kills their helmsman, the ship crashes.
- Elemental Rock-Paper-Scissors: The distribution of Fire (suns) and Earth (planets) especially, determined the structure of a system, and the fact that Air tended to "stick" to objects and people made interplanetary and inter-sphere travel possible.
- The Empire: The campaign-length adventure Under the Dark Fist introduced the Vodoni Empire, a totalitarian and expansionist human empire that controlled no less than twelve solar systems.
- The Emperor: Vulkaran the Dark, overlord of the Vodoni Empire.
- Everything's Better with Penguins: Spelljammer has the Dohwar, a race of telepathic, merchant penguins in SPACE, who ride flying pigs, wear swords on their beaks, and get drunk by eating apples.
- Expy: A lot of the races are recycled from the aliens from TSR's earlier sci-fi RPG, Star Frontiers. Rastipedes are based on vrusk, hadozee are yazirians, syllix are sathar, and plasmoids are dralasites.
- Fantastic Racism: Not much, given Loads and Loads of Races, but still.
- There's human organization Xenos, guys who hate all other races.
- Elven Imperial Navy are generally benign, but are haughty enough to annoy everyone else (Sindiath Line's readiness to receive less belligerent elves upkeeps this status quo). After which they are loudly aggrieved that it was Unhuman War.
- The branch on the Spelljammer is outright genocidal - planning to engage in a war of extermination against all goblinoids that is not portrayed favorably just because they're evil - but is fortunately prevented from actually acting on it by, well, being on the Spelljammer.
- Normal gnomes tend to think that tinker gnomes make the whole race look like clowns; a few of them even go so far as to hunt down tinker gnomes' "ships" to wipe this dishonour off the space lanes. It's not that tinker gnomes weren't generally nice guys, but since minoi mashup machines are plain dangerous for any settlements they may try to land at, those who break them up before they fall on people's heads are at least as likely to be approved as condemned.
- Beholders always run on this trope, but here they can engage in their pointless race wars in full view of everyone else with entire fleets going at it.
- Fantasy Kitchen Sink: and admits this (and encourages in others):
...the writer once described his own campaign as a "cosmic vacuum cleaner, sucking up every fantasy idea that crossed its path."
- Forgotten Superweapon: Second Unhuman War has elements of the Forgotten Super Arms Race, so to speak.
- Good Guy Bar: The World Serpent Inn mentioned in several sourcebooks was built in its own demiplane by an archmage from Toril, Arcane and Illithid as a neutral ground when Sigil turned out to be too violent and inconvenient for quiet business and rest. Not only is it connected to many worlds, but is accessible to powers, and some gods visit it to relax and chat with creatures they deem interesting. It's a Good Guy Bar since no one wants to annoy peacefully grazing deities, and some clients in a common room can turn out to be gods on a tea-break. And even if there aren't any, The Bartender is an avatar himself—if some god just likes to meet new people and thinks it's funny, why not?
- Grey and Gray Morality: Scro vs. IEN frequently approaches this. Scro are Lawful Evil but honorable in their own way and elves are theoretically Good Guys, but they're official jerks who frequently poke into other people's business. Both think that a piratical attack on a neutral party is perfectly acceptable if there's a little chance to get the strategical advantage from it. In the Cloakmaster Cycle some IEN guys even topped it with a random murder just to show they're serious about it. While acting offended that others weren't too eager to join their side in the First Unhuman War, no less. Both try to control all the wildspace as they see fit; and as far as other races are concerned, neither the idea of bloodthirsty scro collecting tribute nor excitable haughty elves snooping around makes for a particularly ideal situation.
- Honest John's Dealership: Rastipede. They are also eager to take an advantage of a client's gullibility while sticking with the letter of bargain only. Arcane are even greater traders, but they are reliable... though not above using rastipede go-betweens while knowing their habits.
- Human Resources: The infamous Lifejammers and Death Helms operate by using the life force of a victim strapped into it to power the ship. They're a favorite of neogi and other evil spacefarers.
- Humongous Mecha: Elven Spirit Warriors, giant undead artificially-grown insect bodies controlled by a pilot in the torso.
- I Am Not Shazam: Sort of--the Spelljammer is a legendary Living Ship, spelljamming helms are the phlebotinum that powers space travel, and spelljammers can refer to ships (usually just "'jamming vessels") or sailors (as opposed to landlubbers, er, groundlings). Or only helmsmen.
Jeff Grubb: In the game we used it to describe the act of moving through space magically. And it was the class of ship that moved through space. And it was the proper name of the legendary Spelljammer, a supposed Flying Dutchman/White Whale. It was a noun, a proper noun, and a verb. If I could have made it an adverb I would have done that as well.
- Living Ship: Though, technically, this was supposed to refer almost exclusively to the titular Spelljammer, it is applicable in a much less interesting fashion to the Elven vessels, which are shaped from a living spacefaring plant. Reigar Esthetics are more potentially dangerous as a lifeform, though just as mindless. Borderline cases are Tick - Neogi vehicle powered by life draining, designed to be used as a "saddle" for something big. And some people just live on the backs of kindori—they are big enough for a village and travel in herds.
- Loads and Loads of Races: That's a lot of people collected from most D&D setting and then some more.
Gaeadrelle Goldring, half-kender on the Rock of Bral: I used to think that a lizard was a lizard, you know, but then I saw that there were as many types of them as there are of people like us. I met some trogs once, not very friendly ones at that, and, wow, did they ever stink. It was incredible. Then I met dracons, saurials, sithp'k, and, of course, the wasag, like that little blue guy over there.
- MacGyvering: Nearly everything ever made by tinker gnomes.
- Mad Artist: The Reigar. Every last one. Add a spoon of Mad Scientist and two drops of Parody Sue, shake until it tastes great and mildly scary.
- Mad Doctor: meets Be Careful What You Wish For in the Xixchil. An ideal choice to acquaint all munchkins in range with, and see what sort of Hilarity Ensues.
- Made of Phlebotinum: This setting as a whole.
- Magitek: Crops up here and there, with the likes of Autognomes (whose malfunctions can be either hilarious or horrifying), and Clockwork Horrors, a race of mechanical spider-like robots that can strip a world of all life over a couple centuries.
- Massive Multiplayer Crossover
- The Multiverse: The characters travel between Crystal Spheres, each containing a solar system or some variant thereof. Basically, every non-scientific legend of what the stars and planets are wind up being literally true in at least one crystal sphere. Additionally, Spelljammer took place within the greater multiverse featured in Planescape.
- Moral Event Horizon: Using Witchlight Marauders. Or just living a normal life of a Neogi (surprisingly, it's not so simple even with mindflayers).
- Ninja Pirate Zombie Robot: Lots of. See also the footnote on Giant Space Hamsters above.
- Organic Technology: Several, elves are best known, as the creators of Bionoids and transport modifications of starfly plant (gadabout, flitter/man-o-war/armada). Reigar at least made their Esthetics and changed Lakshu to their current form. Goblinoid races once made Witchlight Marauders.
- Our Dwarves Are All the Same: They live in giant space stations carved out of asteroids, with surface often sculpted to look like bearded faces. But the dwarves themselves are the same.
- Our Elves Are Better: The Imperial Elven Navy was a vast but loose empire of elves made up of almost every known subrace from many D&D settings. The IEN was a sovereign entity with its own leadership, but it kept groundling elf nations in touch with each other.
- The Spacefaring Elves had the unpleasant characteristics of their landbound cousins turned Up to Eleven. They were haughty, aloof, snobbish and though of everyone else as semi-civilized smelly yokels. They were supposed to play the role that the Spanish/British Navy do play in swashbuckling fiction.
Rozloom: Please, Captain, you see before you a man in great danger.
Rozloom: This one calls you "sir". An elf shows you respect? If you are not great captain, you must be small god.
- Our Gnomes Are Weirder: Hoo boy are they.
- Our Orcs Are Different: The scro - although bloodthirsty, xenophobic, and all-around unpleasant - are quite intelligent, disciplined, honorable after a fashion, and verge on being "Blizzard orcs".
- They were the result of goblinkind races being almost totally expunged from the spelljamming space by the Elven Armadas and hence turning to strict discipline and regimentation to make a comeback - Roaring Rampage of Revenge, literally. Some of them learned to speak Elvish well just so they could properly tell the elves who was killing them. The comeback of the Scro formed the centerpiece of early editions of Spelljammer, with adventures including death star-like Scro stations which looked like Gamera and the "good" races of the setting having to put aside differences to fight the common threat.
- Our Monsters Are Different: There were whole new manuals about D&D species adapted to "Wildspace", and a few unique to the setting.
- Mindflayers and Beholders, already moderately popular in normal settings, were elevated to new heights of villanous complexity, while the Neogi, a cross between a moray eel and a goat-sized tarantula were introduced to serve as reavers and slave traders.
- Powered by a Forsaken Child: Lifejammers tap the life force of living beings to power vessels. Employed by Neogi and other evil spacefaring races. Death Helms do the same, but operate much like a normal helm - the pilot stays on the seat voluntarily (as in, gets addicted by charm) until forcibly removed or falls off it as a withered husk.
- Proud Merchant Race: The Arcane.
- Rube Goldberg Device: Nearly everything ever made by tinker gnomes.
- Rule of Cool: This trumps science every time. Though consistency beats it.
- Say What? There IS a planet full of giant lizards which are treated as the Tarrasque. EVERY. ONE. OF. THEM. And did I mention said planet is full of them?
- The good news is that they're completely docile lithovores... as long as they stay on that planet. It's suggested that the more familiar versions of the Tarrasque are what happen when they're relocated to other worlds, with atmospheres that don't keep them from going homicidally insane.
- Say What? There IS a planet full of giant lizards which are treated as the Tarrasque. EVERY. ONE. OF. THEM. And did I mention said planet is full of them?
- Sapient Ship: "the Spelljammer". It also spawns little cute Smalljammers—unarmed, but very agile living boats capable of empathic contact and magical mimicry.
- Sdrawkcab Name: Scro.
- Secondary Fire: Catapults can throw stones - or scattershot. Jettisons can throw scattershot - or dump debris fields.
- Short-Range Shotgun: Jettisons, special anti-personnel weapons that fire slow clouds of debris. A good thing to use on pursuers ready for boarding, but useless in long range combat.
- Shout-Out: Dolphin: the ship with a detachable shuttle on top of an extended curved "neck"? Hmm, what this strange construction could possibly resemble?..
- One fan theory is that the Rock of Bral is a shout out to Cosmic Boy from the Legion of Super-Heroes, whose real name is Rokk Krinn of Braal. This in-joke was almost almost certainly done because of Rokk's last name being the same as the name of the Dragonlance planet, Krynn. Jeff Grubb's blog, however, mentions that its origin is simply the "Rock of GiBRALtar".
- Shrouded in Myth: The Spelljammer itself.
- Space Is Magic: Literally.
- Space Is an Ocean: With ships, barnacles, and, well...
- Space Pirates: Naturally. One variety is the "Pirates of Gith", who use hit-and-run tactics including temporarily shifting to another plane of existence.
- Space Sailing
- Space Whale: ...space dolphins and space sharks and an echinoderm or whatever those Esthetics are. And the eponymous Space Manta Ray.
- and giant space hamsters
- Space X: Many variant monsters. The best known would likely be "giant space hamster" thanks to the nod in Baldur's Gate.
- Unit Confusion: More than a whole army of umber hulks could make. Those "space tons", dagnabbit. In one Sourcebook a mass of 1 ton allows an atmosphere of 100 cu.yd. of air, in another it means body's own displacement of 100 cu.yd., so...
- Viral Transformation: Aside of usual (The Undead): Bionoid, an artifical Shapeshifting Person of Mass Destruction can also be created by infection, as some eggs are still stashed here and there. Did we already mentioned that elves are nice guys?
- The Wall Around the World: Crystal shells.
- Weapon of Mass Destruction: Witchlight Marauders—a weaponized artifical Horde of Alien Locusts whose only purpose in their life is to eradicate all biomass on a world and die, in preperation for terraforming a world by an invading race. Using them is generally considered a Moral Event Horizon.
- There are mentions of beholders building a giantic weapon resembling an eye the size of a small moon. This eye was capable of destroying entire worlds...
- Weird Science: The gnomes! Who happen to be a branch of the tinker gnomes from Dragonlance who found a way into space but never found a way back down...
- What Measure Is a Non-Human?: Most humans - except Xenos, the club for rabid xenophobes - resigned such worries facing Loads and Loads of Races. Usually it's "What Measure Is A Non Elf": not only they remained true to their habits, but the strong fleet allows them to feel superior (and be asses about this) even more than usual.
- ...which, of course, usually "helps" to unite even more people in disliking them than their more aggressive actions.
bionoid: Because we are living beings and not intelligent, undead weapons, the elves consider us a mistake. Elves, as a rule, prefer not to acknowledge their mistakes.
- A Wizard Did It: The setting runs on this trope. As one source book put it, "It's magic, and it knows it's magic."
- World Shapes: All and any. Mostly, planets in solar systems, but even these got tons of quirks.
The specific stories and accesories contain the following
- Clingy MacGuffin: The Cloak that Teldin Moore gets at the beginning of The Cloakmaster Cycle.
- Cool Horse: Comet steeds. A timid herbivore (after all, they would need to fight only something they can't outrun). Rather smart - for a horse, that is. Trails sparkles. Fast enough to make interplanetary travel practicable (only 1 point below Ol' Manta herself).
- Earthshattering Kaboom: In the First Unhuman War at least one planet was blasted into asteroid cluster. By elves, of course (the Shattering of Borka). The Reigar blew up their homeworld in some sort of performance.
- Farm Boy: Teldin Moore, well, he is not exactly a boy anymore, being in his early thirties when the first book begins, but he still fits the trope.
- Half-Human Hybrid: And not just any, but a half-kender.
- Hollow World: Herdspace, described in The Maelstrom's Eye by Roger E. Moore got an inhabitable landscape on its internal surface. Oh, it's rather small... for a crystal sphere.
- I Am Dying Please Take My Macguffin: The Cloakmaster Cycle starts this way.
- Magnetic Plot Device: an Ultimate Helm.
- That's the magic item that lets you control the Spelljammer, for those of you who don't know.
- My Species Doth Protest Too Much: The Cloakmaster Cycle and at least one Sourcebook has one honorable and even rather nice... mindflayer.
- Obvious Beta: Spelljammer: Pirates of Realmspace wasn't too buggy, but has a great deal of stuff obviously cut short with an axe.
- That's No Moon: That big lake on the map in Herdspace... "Looks like something stepped there, doesn't it?".
- Including breeds like the Subterranean Giant Space Hamster, Sabre-toothed Giant Space Hamster, Rather Wild Giant Space Hamster, Invisible Giant Space Hamster, Sylvan (or Jungle) Giant Space Hamster, Miniature Giant Space Hamster (otherwise known as...a hamster; the breeding came full circle...), Armor Plated Giant Space Hamster, Yellow Musk Giant Space Hamster, Ethereal Giant Space Hamster, Carnivorous Flying Giant Space Hamster, Two-Headed Lernaean Bombardier Giant Space Hamster, Two-Faced Giant Space Lagan Hamster, Fire-breathing Phase Doppleganger Giant Space Hamster, Great Horned Giant Space Hamster, Abominable Giant Space Hamster, Tyrannohamsterus Rex, and the legendary Giant Space Hamster of Ill Omen. ...See?