1. Wormux : Funny animals fight on a 2D map with funny weapons. This game is multiplayer and is highly addictive. Windows, OS X, Linux

2. Nimah : A fairly new game I consider really well done. Art is fantastic, it's open allowing users to create missions, and game play is straight forward. Your goal is to move Nimuh to the next level without getting caught. Windows, OS X, Linux

3. Those Funny Funguloids : Arcade action similar to asteroids interface. The object is to collect floating mushrooms and return them to your mother ship. Windows and Linux versions available.

4. Dreamchess : Simply 3-D chess. Windows, OS X, Linux

5. Neverball and Neverputt : Neverputt comes with Neverball. Neverball is a rolling marble game where you control the ball by tilting the floor. I personally prefer Neverputt, which is the best Putt Putt I have ever played on the computer. Users can create levels. Windows, OS X, Linux

It is really hard limiting to just five, damn it! I have to add some classics!

1. PySol : In my opinion the best cross platform solitaire game ever and written in Python no less!  Windows, OS X, Linux

2. Foobillard : Very well done 3-D pool. Linux mainly, but Windows and OS X ports are available; although, they may be older versions. 

3. Frozen Bubble : This has to be one of my all time favorites and a major classic. It's one of the first Linux games that made me interested in playing games on Linux, if that makes sense. The goal is to shoot marbles from the ceiling before it touches you. The ceiling moves down one each time you shot. Windows, OS X, Linux

4. CromiumB.S.U. : Another classic! Fast paced arcade space shooter. Windows, OS X, Linux 

5. lbreakout2 : Breakout game. Nothing really special just fun game play. Windows, OS X, Linux 

 Have fun!