Bad AR:SE is a set of free wargames rules for modern skirmishes.
rules
Over The Hills and Far Away
Over the Hills and Far Away is a regimental campaign game from the fertile gaming mind of Jim Wallman.
FUBAR Medieval Rules
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 Racing Game
Dunger Derby is a miniatures game of racing little wasteland beasties called Dungers. You really have to take a look to get it.