Back in August I mentioned TORCS. Speed Dreams is a fork of TORCS that aims to implement exciting new features, cars, tracks and AI opponents for a more enjoyable game for the player, plus constantly improving visual and physics realism.
Written in C++, there are versions for Windows, Linux and soon Mac. As it's open source you can always download the code and compile it yourself if your OS isn't there. As with many open source projects, they are always looking for developers and contributors. See their Wiki for more details if you are interested.
- Permananent link added to C++ Games Code library