Earth Delta RPG

Earth Delta is a sci-fi RPG trying to capture an old-style vibe. The author has some interesting design goals:

Before we launch into any actual rules, it’s probably a good idea to clearly state some design goals. The goals of Earth Delta are:
 Capture the spirit of old-style Gamma World, especially the first and second editions, and of the sources which inspired it or which seemed to draw inspiration from it: Hiero’s Journey, Heinlein’s Orphans Of The Sky, Metamorphosis Alpha, Kamandi, Thundarr, Wasteland, Fallout, and anything else with mutants and mayhem.
 Create a game which is balanced and playable. This isn’t a beer-and-pretzels game (though it can be) or one where you create “wacky” throwaway characters. Nor is it one where random luck determines if you’re useful. One of the Unchanged is just as powerful as a winged grizzly bear with laser eyes.
 Allow for the playing of winged grizzly bears with laser eyes.
 Be balanced with standard 4e rules, so there’s minimal work involved in taking creatures, or characters, from this game into D&D.

Firefly For Savage Worlds

Here’s an excellent adaptation of Savage Worlds to the FireFly universe. I’m a fan of the all-too-short-lived Josh Whedon science fiction series.

Space Rat RPG

Space Rat is an RPG written by Nathan Russell in just 24 hours. It’s inspired by the cheesy science fiction movies of the 70s. It looks like a lot of fun.

Legends of Time and Space RPG

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d20 Barsoom Variant

Edgar Rice Burroughs’ Barsoom novels are among my favorite guilty pleasures. Sean K. Reynolds has a page with material, including monster and character profiles from his d20 Barsoon campaign.