If you follow our planet, this is no news, but the recent advances in graphics, networking a other stuff from SuperTuxKart are quite nice. This is basically a result of them being accepted to this years Google Summer of Code.
Not showing most of the new features yet is this nice video featuring the mascot of OpenGameArt.org as a new player character:
But their blog has many interesting technical details (and other screenshots + videos) to show off the new features.
So if you like to also contribute, or just want to praise the great work, have a look at their FreeGamer hosted forums