Open Adventure is a free, open-source old school role playing game. From the description:
Open Adventure is a full-featured tabletop adventure game that offers out-of-box support for medieval fantasy and science-fiction expeditions. In Open Adventure, you play as a heroic or villainous figure free to explore the perilous world created by the all-mighty Game Master. Along your adventure you’ll battle ferocious enemies, solve complex puzzles, navigate labyrinthine mazes–and much more!
Cybercity Blues is a free RPG that has a lighter take on the cyberpunk genre. The authors write:
“Cyberblues is a bit like Cyberpunk, only more mellow.”
Cyberblues City is a near-future, action-adventure roleplaying game. Fast-playing and often funny, it offers a lighter take on the cyberpunk genre, both in terms of system and tone. Cyberblues City uses a much modified version of the Fudge roleplaying system designed to make it easy on GMs. And best of all, it is absolutely free.
Legends of Time and Space is a free role playing game that takes its inspiration from Steve Jackson Games’ The Fantasy Trip.
Force Nine is a free science fiction Role Playing Game in the spirit of Aliens.
FORCE 9 is a science-fiction roleplaying game set in a galaxy at war with a bug-like alien menace. The Player Characters are part of a special Space Marine unit assigned to combat the bug Hive Mind before it comsumes all of mankind. FORCE 9 takes much of its inspiration from the Alien films (especially the second), and more recently, Starship Troopers.
FORCE 9 has been designed as a “pamphlet game” – in other words, only the essentials required for play are included here (spiced up a tad with cool graphics, of course). The hardcopy, plain text version of the game should take up no more than nine letter size pages. Future expansions will be provided, detailing other parts of the setting, more Space Marine missions, new equipment and enemies, etc.
FORCE 9 may have grown a little beyond its origins, but it was initially designed as a “beer and pretzels” game – something simple and fun to play as a break from your regular roleplaying. We think it still works great in this respect. Character creation is fast, the setting and tone are familiar to any sci-fi fan, and missions seem to write themselves. If your gaming group finds itself with a free afternoon, don’t pick up those Magic decks, generate some Space Marines and kick alien ass!
A fan of the Doctor Who universe has put together a sourcebook of material for the Third Doctor’s extracanonical adventures from novels, audios, comics and the like. The book is designed to go with the Dr. Who role playing game. It looks very professionally done.