Over the Hills and Far Away is a regimental campaign game from the fertile gaming mind of Jim Wallman.
Following up on their FUBAR modern rules, Gawd ‘elp Us Games offers FUBAR Medievals.
Core Game Development Studios offers a set of free wargames rules called Timeline. From the author: Timeline Skirmish is the skirmish game covering all historical ages and into the far future. This game is meant to be fast and furious.
Dunger Derby is a miniatures game of racing little wasteland beasties called Dungers. You really have to take a look to get it.
Skank Games offers Warlord 2085, a set of free wargames rules for fast play science fiction miniatures.