Warband is a free RPG with a science fantasy, science fiction flavor. In truth, it could very well be the Warhammer 40K RPG. The author writes:
This game is my homage to the ‘grim, dark future’. A game of spikey power armor wearing, bolt-gun shooting, chain-sword waving chaos worshippers. Characters struggle to survive in the warp of space, as low-level members of a Chaos Lord’s warband, they strive to make a name for themselves and eventually captain a ship of their own.
Basic Fantasy is a free RPG system, complete with dozens of modules and supplements. The author writes:
The Basic Fantasy Role-Playing Game is a rules-light game system based on the d20 SRD v3.5, but heavily rewritten with inspiration from early role-playing game systems. It is intended for those who are fans of “oldschool” game mechanics. Basic Fantasy RPG is simple enough for children in perhaps second or third grade to play, yet still has enough depth for adults as well.
This is a major work.
My perusal of blogs tells me that a lot of miniature gamers now are running rpg style miniatures games with rules sets like Conan!, Song of XXX and In Her Majesty’s name among others. For people running Conan style games, here’s a great list of treasures / objectives.
The Corrupt Crypt of Ilmater is a free dungeon adventure for parties of level 4 – 6. It’s designed for old school D&D adventures, and comes complete with the classic blue maps.
Lamentations of the Flame Princess is an old school RPG of “fantasy adventure and horror.” The link is to the free version without illustrations. The illustrated version apparently has some rather adult and disturbing illustrations.