SuperTuxKart is an open source clone of the classic Super Mario Kart. You race as Penguin, Yeti or similar in karts on different tracks. On the route you will find all sorts of useful and harmful things. An anvil for example slows your speed down so that you have little chance to beat your opponent.
In the current version, a launcher is included, which allows you to start the software in Mac OS X as used to.
A tutorial for installing you can find at Free Mac Software Wiki