Silent Dark (direct download link) is a set of free wargames rules for “tactical” science fiction games.
The Miniature Wargaming Editor
Swamp Fox American Revolution Campaign Game
The Perfect Captain’s Swamp Fox is a set of rules for American Revolution campaigns.
Hoplomachia Peloponnesian War Rules
Hoplomachia is a set of free wargames rules for the Peloponnesian War.
2d6 Sword and Sorcery
2d6 Sword and Sorcery from Two Hour Wargames is available as a free pdf download. It is designed as a beer-and-pretzels style adventure game.