From Warspawn Games: Celtic Skirmish, a combination miniatures / board game.
Rules: Ancients
Nauta Ancient Naval Wargame Rules
Nauta is a set of free miniature wargames rules for playing out ancient naval battles. The files are hosted here:
Bible Bashers Ancient Skirmish Wargaming Rules
Bible Bashers is a set of free wargames rules for skirmishes in the bronze age.
Blades of Bronze Ancient Skirmish Rules
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 Roman Age Game
Sandarticus is a set of free wargames rules for backyard and sandbox games featuring Romans and their numerous adversaries.