KarBOOM is a bitesize freeware treat about some lovely little cars indulging in a spot of sumo wrestling on a high plateau above a bottomless drop. It supports internet and local multiplayer, the latter a ridiculous attempt in trying to fit four desperate hands on one keyboard, each sweating to control the adorable wind up bumper cars as they fight their way through a bevvy of game mutators that work much in the same way as Unreal Tournament handles things.
In development since late 2010 and seeing regular updates driven by community feedback, it's an easy spot of fun. The driving model skips merrily between "Oh yeah, I got this" to "Oh god I'm totally out of control please stop I want to get off", usually whenever the Boost mutator is in effect.
KarBOOM is eminently customisable, allowing you to fiddle with all manner of victory conditions, bots and mutators. It just barely works at times, the merry chaos in the latest update supporting up to 48 cars in the same arena, in as much as that madness is actually playable (it's not).
Follow the fun over at the official page.