Njam :: http://njam.sourceforge.net
Pacman clone. Can go multiplayer via LAN. The first one is free on Linux only. A second one was released as paid software for Windows. Njam 2 players could LAN with Njam 1 (hence cross-platform). Would it be possible with the Zero, I wonder...
Secret Maryo Chronicles :: http://www.secretmaryo.org
One of my favorite Mario clones. Has a level editor (in which is better off to be used on a computer anyway). It would be possible to create levels and share them to other potential Zero users.
Armagetron :: http://armagetronad.org
3D light-cycle (Tron) game. Again, would be interesting to do this via LAN.