Fire and Forget Games has released a downloadable PDF version of the rules for Faction Wars, the sci-fi skirmish game. The free 40-page PDF contains the basic rules of the game, sample squads for two factions, and a couple of scenarios to get you started.
science fiction
Mobile Suit (MS) Era Rules
MS Era is a set of free wargames rules for playing with those Mobile Suit Gundam figurines.
Raum Krieg
Raum Krieg is set in an alternate history where Germany and the Allies battle it out in the skies with UFO Technology.
Starcraft Tactical Miniatures Combat
The Starcraft Tactical Miniatures Combat rules are based on the world of the classic video game. I suppose you could use miniatures from the board game to play.
Tacship Space Fighter Combat Rules
Tacship is a set of free wargames rules for space combat by John Tuffley. He writes:
Tacship is a simplified fast-play rules system for simulating combat between manned space fighters. The game may be played on a hex grid map or on a plain table area by substituting inches for hexes and measuring turns in 60 degree increments (the same as a one hexside facing change). Fighter models should be mounted on stands, preferably with a one inch hex base, if a grid is being used.