GHQ has a free pdf of its Beer and Pretzels Modern Micro Armor game, formerly a commercial effort, now a set of free wargames rules.
Miniatures Rules
Trireme Game Rules
The Trireme Battles blog offers a set of free wargames rules for trireme battles.
Beer and Pretzels WWII Micro Armor
GHQ has a pdf of its Beer and Pretzels WWII Micro Armor, originally a commerial set, now a set of free wargames rules.
Escaramouche Pike and Shot Era Skirmish Rules
Escaramouche is a set of free wargames rules for skirmishes in the Pike and Shot era. It’s designed to be played with perhaps six figures per side.
Reconstructed Sweet Home Rules For Ancient Battles
Blunders on the Danube Blog has a set of free wargames rules for ancients battles based on Charles Sweet’s classic set.