Sunder The Stars is a set of free wargames rules for Starship Combat.
Space Fury are a set of quick and dirty space fighter combat rules.
One Page Fleet is Mike Wikan’s set of free wargames rules for starship combat.
Tom’s Spaceship Miniatures / Games List offers a nice resource for people getting into this type of gaming. FWIW, Silent Death is one of my all time favorite games.
Event Horizon is a set of free wargames rules for quick play starship combat. It is played on a grid board.