Battleshift is a set of space fleet combat rules for big fleet battles.
Miniatures Rules
Pulp Action Miniatures Rules
Dadie Piombo has a set of basic rules for playing Pulp Action miniatures games.
Lights In The Sky Starship Battles
Lights in The Sky is a set of free wargames rules for space battles.
Steve’s Horse and Musket Rules
Steve’s Horse and Musket Rules are designed to be a simple set of rules emphasizing the three arms (horse, foot, guns) and command.
Trenched Rules
Trenched is a set of free wargames rules for squad level combat. In spite of the name, it is not a WWI rules set. The example photos are of Warzone science fiction figures.