Greater Space Battles is a set of solo rules for space battles using miniatures from Solipsist Games.
War In Space is a set of free wargames rules for star ship combat. What makes it different is that it uses standard playing cards for giving orders.
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.
Full Thrust Cross Dimensions is a Full Thrust rules variant. It brings together rules from the various books and tries out some new ideas.
Hostile Stars is a set of free wargames rules for fighting fleet actions in the Dark Realms universe.