Nauta is a set of free miniature wargames rules for playing out ancient naval battles. The files are hosted here:
Bible Bashers is a set of free wargames rules for skirmishes in the bronze age.
Blades of Bronze is a set of free wargames rules designed for short skirmish 15mm ancient wargames. The rules revolve around the ability of the leaders to give orders to the troops.
Sandarticus is a set of free wargames rules for backyard and sandbox games featuring Romans and their numerous adversaries.
Castle Cracker is a set of free wargames rules for backyard games in the ancient and medieval eras.