Full Thrust is an excellent set of starship combat rules — my personal favorite, in fact. Here are a set of modifications and statistics for playing Star Wars battles.
rules
Thumbs Up, Thumbs Down Gladiator Rules
Thumbs Up, Thumbs Down is a set of free wargames rules for gladiatorial combat. The rules are designed for up to ten players.
Dinky Dau Vietnam Rules
Dinky Dau is a set of free wargames rules for skirmishes games set in Vietnam.
MuTaTioR Le choc des MuTaNs (Mutants: Shock of the Titans)
MuTaTioR Le choc des MuTaNs (Mutants: Shock of the Titans — that’s as close as I can get the translation) is a set of free wargames rules in French for combat between mutants in an arena. Google translate does a pretty good job of making sense of this in other languages. One great thing is that it includes rules for creating mutants — shades of Gamma World and to some extent, GW’s Realms of Chaos (I vaguely remember creating mutants for that game).
Big Burn Fleet Actions
Big Burn is a set of free wargames rules for fleet actions in space.