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.
Role Playing Game
Mutant Future RPG
Mutant Future is a retro-clone of the old TSR Gamma World Game. There’s a commercially available printed version, but you can also download an artless version if you just want the rules.
Call of Cthulhu Quick Start Rules
Call of Cthulhu is one of the great role playing games. There is a set of free quick start rules available on RPG Now.
Mutants and Machine Guns RPG
Mutants and Machine Guns is a free RPG set in a post apocalyptic future. It is simple enough that it fits into the terrific PocketMod format.
Icar Science Fiction Role Playing Game
Icar is a science fiction RPG with an intriguing setting:
Icar is a space opera set in the 93rd Millenium. Since leaving Earth, the human race has been through a number of social catastrophes, including the cliche of creating a humanoid race of robots which fought back against their creators. The Imperium, a benevolent organisation, steers the human race to keep it alive.
Take the part of a Scavenger crew exploring deep space for the chance of finding expensive salvage, step into the shoes of a Special Forces team up against the odds, fight crime through the eyes of a policeman as part of the most high-tech police force ever know or just create your own characters to explore this detail rich universe.
The author has been working on this since 1990 and the game is now in its umpteenth revision.