FooBillard is a free billiards game for Linux. The graphics are nice and it features realistic physics. You can play against an AI or play two players. There are several game types to choose from, 8 ball, 9 ball, carambol and snooker. It is also possible to change the size of the pool table. It is a 3D game with detailed textures. Here is a link to the FooBillard page.