The Die is Cast is a set of free wargames rules For The Battle of Pharsalus (48 BC), a decisive engagement between Caesar and Pompey.
Miniatures Rules
Mike Mike Projectile Wargaming
Mike Mike Projectile Wargaming is a set of free wargames rules for games of that sort where you use some short of shooter (such as a rubber band gun) to knock over the figures.
Use with plastic only.
The Portable Wargame: Ancients
The Portable Wargame: Ancients is a set of free wargames rules for ancients wargames using a gridded surface and individually based figures. The Ancients version is one of several using the same system in different periods.
Flip It Paper Combat
From the authors:
Flipit: Paper Combat is a fast-paced tabletop miniatures game in a setting similar to WWII. Players lead forces from one of the four major nations into the conflict for Jurop. Armies are built of models players can download, print and build for almost free (you still have to supply the ink, paper, and glue). There are simple starter rules available, which may be supplimented by optional advanced rules to make gameplay more challenging
Hat Tip to Martyn for the link.