Gamma World

A classic role-playing game originally created by TSR, the same people who made Dungeons and Dragons. Centuries after a vaguely defined apocalypse, a radioactive and ruin-strewn Earth is inhabited by mutants, sentient animals and plants, and insane half-functioning robots, all of whom compete for influence as multi-species civilization begins its long climb to recovery. Gamma World was heavily influenced by TSR's earlier sci-fi RPG, Metamorphosis Alpha.

Despite what a newcomer might think, the tone is quite light-hearted, and the players are strongly encouraged to have fun and not think too hard about how silly it all is.

The game has gone through seven editions so far; TSR published the first three from 1978 to 1985 with their own unique rule sets. 1992's 4th Edition was based on the same engine as D&D's 2nd edition, and 1995's 5th was a supplement for the sci-fi RPG Alternity. In 2002, Wizards of the Coast, which had since absorbed TSR, published a wacky homage to Gamma World entitled Omega World in Polyhedron magazine.

The setting was licensed by Sword & Sorcery Studios (a subsidiary of White Wolf) and heavily revised for D20 Modern in 2003. This new edition recasts the apocalypse as a war among post-Singularity civilizations, a horrific spasm of nanotechnological and biological warfare (with a few nukes thrown in for old time's sake). The old creatures and robots are nearly all retained, but given new and detailed explanations that are designed to elicit horror and awe rather than cheap jokes.

Wizards of the Coast has since released a seventh edition of Gamma World, using the 4th edition Dungeons and Dragons rules, in October 2010. The game is far more humorous, from character creation, to Omega Tech descriptions. The 7th Edition setting is one where "the Big Mistake" merged all possible worlds into one, and really leaves the door open for player interpretation.

Gamma World is notable for one rather odd trend: usually, only a handful of books would be released before a new edition came out and rendered all the previous books obsolete. This reached its zenith with the Alternity version, which had only a single, core rulebook released before being discontinued. Time will tell if 7th Edition will continue this trend.

This game includes examples of

 * Adam and or Eve
 * Adaptation Distillation: Omega World, a tribute to the original game.
 * Adventure Towns
 * After the End
 * All the Myriad Ways: The seventh edition backstory features the Large Hadron Collider causing several different realities to intermingle and exchange places, in an event called "the big mistake". Furthermore, Dopplegangers create their doubles by pulling them out of alternate realites.
 * Amazing Technicolor Population: Antimatter Blasters are blue, Demons are red, and Photonics come in shiny red, blue, or green.
 * Ancient Conspiracy
 * Apocalypse How: Class 2
 * Atomic Superpowers
 * Beast Men
 * Big Creepy-Crawlies: Cockroaches and Arachnoids.
 * Bigfoot, Sasquatch, and Yeti: Yetis.
 * Everything's Better with Monkeys: Simians.
 * Everything's Squishier with Cephalopods: Octopoids.
 * Lizard Folk: Saurians.
 * Winged Humanoid: Hawkoids
 * Brain In a Jar: Borgs, Permanent Cybernetic Installations and Think Tanks in 1st Edition.
 * Chameleon Camouflage: The Chameleon Powers mutation in the 1E game.
 * City in a Bottle
 * Collectible Card Game: 7th edition has its powers and technology sold on this model; GMs and players have to buy more cards in booster packs for more fantastic stuff to use in their RPG, instead of buying them in sourcebooks. This has not been well received.
 * The core game does include include a full deck of mutations and Omega Tech (Loot), so players aren't forced to go out and buy boosters. The boosters certainly don't have anything that's any more game-breaking than what you get in the core box.
 * Crapsack World
 * Crystal Dragon Jesus
 * Darker and Edgier: The 6th Edition for D20 Modern.
 * The original game when it first came out. Its said to have popularized dark humor in RPGs.
 * Duct Tape for Everything: We're sure you'll find a use for this...
 * Everything's Worse with Bears Who Think They Are Napoleon
 * Fantastic Racism: The Knights of Genetic Purity, the Iron Society, the Zoopremicists...the list goes on.
 * Horn Attack: Mutant characters could have horns as a mutation. The mutants known as Rakoxen (and Hoppers in 2nd Edition) had them.
 * Horse of a Different Color: Mutant horses, giant horses, podogs, cactus horses...
 * I Love Nuclear Power
 * Improbable Weapon User: Since the game is set in a Scavenger World, it is almost a given that your characters will be these. You could wield a stop sign, a telephone pole, vending machines...really anything you can think of that fits within the one-handed/two-handed light/heavy melee/ranged parameters.
 * Killer Robot: Technically could be your player character. The Created are an entire faction made of Killer Robots.
 * Light'Em Up: Photonic origins.
 * Lost Technology
 * Machine Worship
 * Make Me Wanna Shout: The 1E Sonic Attack Ability mutation.
 * Mutants
 * Nanomachines
 * Ninja Pirate Zombie Robot: Because you can choose two origins for your character, and the origins are each quite different, you can end up with lots of these. Android Plants, Vampire Octopoids, a hoard of tiny yetis...
 * Plant Person
 * Playing with Fire
 * Psychic Block Defense
 * Ragnarok Proofing
 * Recycled in Space: It's D&D, but After the End ! AND SILLY !
 * Rule of Cool
 * Rule of Fun
 * Scavenger World
 * Shrouded in Myth: The world before the Cataclysm. Old technology are known as artifacts, electricty is called lightning and machinery, particularly robots, are called live metal.
 * Sickly Green Glow
 * Sliding Scale of Silliness Versus Seriousness: The original game, 4th edition, and Omega World are so far on the silly scale that it mutates and flies out into space. 3rd edition and 6th edition, on the other hand, land on the more serious part of the scale, but not to the very end.
 * 7th Edition is much closer to the silly end, including a suggestion that you could respond to a villain by pulling out a cane and singing and dancing like Michigan J. Frog, a backstory in which Peshtigo, Wisconsin suffered nuclear annihilation by the French an untold number of times over (it's said to have happened in 3% of the originally-separate universes that combined into Gamma Terra), random shout-outs to virtually everything under the sun, and not even an attempt to make the yexil (Basically cloth-eating anthropomorphic manticore bandits with laser eyes—no, really) or the other more bizarre monsters anything except completely ridiculous.
 * Sliding Scale of Turn Realism: Round by Round.
 * Spare Body Parts
 * Super-Powered Robot Meter Maids: Literally.
 * Swiss Army Weapon: The Chameleon Rifle in module GW6 Alpha Factor.
 * The Worm That Walks: One of the possible character origins. Depending on your primary origin and your secondary origin, you could be anything from a horde of cockroaches, to a mass of nanomachines, to a horde of sentient, hive-minded kittens.
 * Wetware CPU: Androids. Inverted with A Is.
 * When Trees Attack: Plants are a possible character origin in all of the editions. Also there have always been numerous species of plant-monsters to spice up wilderness adventures.
 * You Fail Nuclear Physics Forever
 * X Meets Y: D&D meets Fallout.