excido is a free (GPL) game. It combines (simple|old school|arcadey) gameplay
with 3D OpenGL graphics and OpenAL positional audio. Excido is not a
highly complex experience, but you may enjoy it as a small diversion.

Excido was developed under GNU/Linux, and has also been found to work on MacOS
X. It should also work with minimal porting effort on the other platforms
supported by SDL/OpenAL.