Check out the skills of atphalix who has taken on the technical challenge of overcoming the physical & hardware limitations of the XO Laptop hardware (no OpenGL hardware 3D acceleration) to get Quake on the XO laptop:

Now atphalix is seeking a higher goal than a better Doom on the XO experience, he's using Quake to make a true 3D educational game with software rendering only. ABC Cube consists of shooting cubes with letters/numbers on them, with the letter or the number pronounced at each kill, to facilitate memorization.

Before you condemn the violent nature of atphalix's chosen application, listen to why he picked Quake and his overall goal:

The Quake 1 game engine was chosen for it's ease of modification and for its network capabilities that would make the project usable as a base for making other kind of innovative 3D games and activities for the laptop. As a matter of fact, success in bringing the 3D to the XO through software rendering would be a great proof of concept as well as a base to start other 3D appliances upon the technical foundations of abcube.

Now I find that quite innovative - using a first-person shooter for a positive, educational experience. If you too like his efforts, here's the OLPC wiki page and OLPC News Forum post.