I just discovered the now defunct Mario Kart Source project. They have released all their assets as open source (without a specific license). I am curious about two things.
They made a couple very nice karts.
http://www.moddb.com/mods/mariokart-sou ... t#imagebox
If I can get them to put a real license to their work and if we reskinned it we could use it? It would need some work to function properly in the game, but that's really nice looking.