Dunger Derby is a miniatures game of racing little wasteland beasties called Dungers. You really have to take a look to get it.
Wasteland Racing is a set of free wargames rules for deadly races in a post apocalyptic world.
Marathon is a fantasy race game where
Players take the roles of Gods, secretly influencing six Heroes as they strive to complete the mythical Marathon race. You must be subtle as you influence your Heroes: once a God’s favorite Heroes are known the other Gods will work to thwart them! At the end of the race, the God whose favorites have moved the furthest wins the game!
GrimDark Racing is a set of simple rules for races in the Warhammer 40K universe. Just use models you already have. There’s plenty of violence, of course.