Starship Marines is a set of free wargames rules for Starship boarding actions. This is quite a detailed set, and is continued in Starship Soldier.
The Miniature Wargaming Editor
Stingray, Stingray, Undersea Rules
Stingray, Stingray is a set of free wargames rules simulating the 1960s television series Stingray.
Fire At Will
Fire At Will is a set of free wargames rules for 6mm fantasy battles.
Air Wars Rules
Air Wars is a set of free wargames rules for air combat in the Vietnam War era.
Tank Duel WWII Rules
Tank Duel is a set of free wargames rules for WWII games where each player commands a single tank.