Taktika is a set of free wargames rules for science fiction battles.
Miniatures Rules
Black Hat, White Hat
Black Hat, White Hat is a set of free wargames rules for Wild West skirmishes.
Universal Combat System
Universal Combat System is a set of free wargame srules described by the authors of being for “any number of players in an infinite amount of settings.”
No Quarter Fantasy Rules
From Chris Gilders comes No Quarter Fantasy Rules. These free wargames rules are a massive work, with 83 pages in the main rules book alone. There also are a large number of army lists, which is the real strength of the set. Like many fantasy games, figures are defined by a model profile, detailing combat stats, actions, strength, toughness and wounds. This is an amazingly comprehensive work for a free rules set, covering every aspect of fantasy warfare you could want.
Paper Models Of Science Fiction MASH Container Units
The TopSolitario website has a paper model of a science fiction Mobile Army Surgical Hospital (MASH) container unit. Its designed for Infinity, but would be useful for any science fiction game.