WarZone, in its original incarnation some twenty years ago, was one of my favorite games. I still have substantial painted armies from that era. Then the game went through a series of owners, rules changes, and model changes. Eventually, it died, only to be resurrected by Prodos. That company has the latest version of the WarZone rules free for the downloading.
science fiction
Frag-O-Rama Skirmish Miniatures Rules
Frag-O-Rama is the “free miniatures game of multi-player, shoot-�em-up, videogame-style action for 2 to 10 players.” It’s also got a blog for discussing the rules development.
44: A Game of Automatic Fear – Free RPG
44: A Game of Automatic Fear is a free rpg set in a 1950s where a conspiracy is replacing humanity with robots.
A Fistful of Sardaukar Dune Miniatures Game
A Fistful of Sardaukar is a set of free wargames rules for battles in the Dune universe of Frank Herbert.
No Limits Science Fiction Rules
No Limits is a set of free wargames rules for tabletop battles in science fiction universes. Any miniatures from any game can be used.