An open source racing game on the Mac!
This is more a great software than a tip, but I think it is worth mentioning. It is an open-source racing game called VDrift. It is entirely free and there is a Mac version. The game has a lot of different cars and tracks and the graphics are very good (from what I can tell, I am not a gamer). Even if you are not a gamer, it is fun once in a while and it also a great entertainment if kids visit sometimes. It lagged a bit on a MacBook, depending on which track. There was absolutely no problem on a Mac Pro with a x1900XT. I think it runs pretty smoothly on any recent Mac that has a graphic card (it will probably lag a bit on the MacBook and Mac Mini). You can download VDrift here on MacUpdate or here on the VDrift website.