4st Attack is a good looking connect-four with multiplayer support. It also has theme/skinnability and a decent AI to hone your skills.

The goal of the game is to connect four pieces of your color in a row. The tricky part is that your oppenent is doing the same thing. And who ever does this first wins.

License: free

Additional System Requirements: < a href="http://www.pygame.org">Pygame(www.pygame.org)
Python(www.python.org)