The second edition Maifaux Rules are available free for the downloading.
Miniatures Rules
Calantsoog Napoleonic Amphibious Assault Board Game
Calantsoog is a free print-and-play board game of Napoleonic amphibious assault. That’s a subject that I don’t think has ever been covered before.
Attack Vector Space Combat Game
Attack Vector is a free tabletop game of space combat.
The Stars Our Decimation: Voidstriker
The Stars Our Decimation: Voidstriker is a set of fleet oriented starship combat rules. They can be used as a board game, and with miniatures and hexless play.
Mobile Frame Zero Lego Rules
Mobile Frame Zero is a set of free wargames rules (although you can pay, too, if you like it and can get a printed version) for playing games using Lego and other construction toys. It is very well done.