GURPS Infinite Worlds

GURPS Infinite Worlds is an alternate history setting for GURPS and the closest thing GURPS has to a "core setting", though oldfags hearing that will grumble into their neckbeards about Banestorm. But Infinite Worlds is in the (4th edition) corebooks and Banestorm isn't, so there.

Infinite Worlds was first created as a campaign frame for GURPS Time Travel in the mists of 3rd edition, and proved sufficiently popular to not only get supplements in the form of the Alternate Earths books, but be promoted to corebook status and have 4th editions's Time Travel supplement named after it. The fact that the mechanics of "time travel" in Infinite Worlds promote buying a lot of GURPS supplements is surely a coincidence.

Parachronics for Dummies

The Infinite Worlds setting draws heavily from H. Beam Piper's "Time Patrol" stories; instead of going backwards in time and potentially screwing up your own future, you physically travel to a parallel universe that just happens to closely resemble your own at some point in the past. This is great for /tg/ purposes because it instantly removes all of the headaches that happen when you give players access to time travel. No leaving yourself the solution to the adventure Bill & Ted style. No hour-long arguments about player characters meeting themselves or "why can't we shoot Hitler?" bullshit. Access to parachronics is strictly controlled, so the party can't go AWOL to find the timeline where genetically engineered catgirl slaves exist instead of playing your campaign.

Parachronics is the means of sending matter from one parallel universe to another within a certain "range". The parallels accessible from parachronics are (almost) all copies of the "prime" universe (called Homeline) where alternate quantum states caused history to turn out slightly differently. In (almost) all of these alternate worldlines time also flows a few billionths of a percent slower, explaining why they're "in the past" compared to Homeline.

Getting there

Parachronics-accessible timelines are clustered into 10 "quanta" in higher-dimensional space. Homeline is in Quantum 5 and can access worlds as far out as Quantum 3 and Quantum 7; the closer the timeline is to Quantum 5 the easier it is to reach.

To send something into another timeline, you can either use a parachronic projector that effectively teleports matter one way or a conveyor that acts as a "time machine" within the same quantum but needs to be boosted across quantum levels by a projector. Parachronic travel effectively telefrags anything at the destination. Parachronic travel also requires a lot of power; conveyors stuck in a strange time without power have to locate a windmill, steam engine, or convenient lightning storm in order to get back.

History

Homeline's timeline diverges from the "real world" in 1985, when Dartmouth physicist Paul Van Zandt discovers parachronics. After mapping out a group of 23 alternate universes, abusing triangular trade to make a shitload of money and blackmailing the United Nations to stay out of his way, he revealed parachronic travel to the world and established Infinity Unlimited to commercialize it, followed by the Infinity Patrol to keep the technology from being abused too much or leaking into the broader multiverse.

This would be hard enough, but things got a lot more complicated 9 years ago, when Infinity Patrol discovered the existence of Centrum, an alternate timeline that is equal parts 1980s dystopia and expanding empire. Centrum is actively trying to take over the multiverse by steering alternate histories to be in line with its own post-post-apocalyptic society, but doesn't have the ability to attack Homeline directly; instead groups of two to five player characters agents wage a shadow war across innumerable timelines to keep history on the respective "right course".

Things got even worse recently, when Reich-5 (one of the many "Nazis win" worlds) discovered SCIENCE!/MAGIC!/PSI! ways to jump timelines. Infinity is now stuck trying to keep Homeline Israel from projecting nukes into Reich-5 and starting an interdimensional war they can't win without ceding the rest of the multiverse to Centrum. This is on top of their normal duties keeping gormless tourists from spilling the secret of parachronic travel, cracking down on smugglers, policing national colonies on timelines where humans never evolved, and keeping an eye open for shitty wizards that might ruin everything anyway.

Notable Known Timelines

• Armada: The Spanish Armada doesn't get pwned in 1588, leading to a Spain-dominated Europe.
• Atilla: Genghis motherfucking Khan decides to destroy the cities of Europe and Asia instead of ruling them, leading to a world of shitty barbarians where only Japan and the Congo have something resembling a medieval civilization.
• Britannica: The British Empire manages to avoid being broken by the American Revolution and continues to rule the world. Centrum loves these assholes, since their world was also run by limey fucks before the bombs dropped.
• Caliph: Literally "the historical progress lost by the Christian Dark Ages." Starts off with much wank about the Abbassids inventing the printing press 500 years early and reaching a "enlightened Islamist" TL11 by the 17th century, immediately redeems itself by exploding into war with a radical secularist state. This is about the upper limit of the level of technology Infinite Worlds can support without breaking; both Centrum and Infinity are torn between trying to loot as much ultra-tech as they can and just boarding up the timeline so they don't get any hints about parachronics existing.
• Campbell: John Campbell dies in a car accident before he starts his science fiction magazine. History ends.
• Dixie: The Confederacy won the Civil War, and they didn't even need jumped-up Afrikaaners with AKs to do it. The US is usually further balkanized or or a European puppet in Dixie worlds.
• Ezcalli: Fuck yeah Aztecs. In this world Carthage discovered America two thousand years early, soon enough for a bunch of pissed off jungle fighters with sharp glass to drive them off, while Europe once again gets buttfucked by Mongols thanks to Rome collapsing more completely than usual.
• Gernsback: Nikola Tesla gets hitched to J.P. Morgan's daughter, leaving both rich enough and sane enough to build all the insane shit Reddit insists he had on the drawing board before the Templars geeked him. Think The Rocketeer and you won't be that far off, with the complication of the world being ruled by a technocratic cabal backed by a monopoly on broadcast power. Infnity has its work cut out for it here because every schlub on Homeline with an electrical engineering degree wants to be the one to invent the transistor.
• Gotha: Zombies? Zombies. These are more the 28 Days Later berserk-cannibal kind than the half-dead Romero kind. The really scary part is that Gotha parallels seem to be multiplying over time.
• Madland: GURPS Fantasy: Adventures in the Mad Lands.
• Johnson's Rome: The tourist trap Rome, which thanks to Marc Antony winning the battle of Actium never quite fell. The tourism company Johnson Crosstime practically owns the Empire and tries very hard to keep this timeline stable and convenient for Homeline visitors.
• Merlin: GURPS Technomancer. Needless to say, nobody wants the timeline with killer penguins getting access to parachronics. (It's too late; the CIA already figured out Gate spells and dropped infiltrators in Homeline, and fascist Argentina has made early contact with Reich-5.)
  • Technomancer has parallels of itself as well. Merlin-2's Hellstorms come from two terrorist nukes in Jerusalem and Galveston that have the Western world running scared, since they've figured out a third nuke would destroy the universe. Merlin-3 is just GURPS Weird War II.
• Enigma: The Ramones never tour England, meaning Mick Jones never formed The Clash. In retaliation, God destroys humanity.