I created a game last week for the One Laptop Per Child XO laptop.
A screenshot of the game running in color:
FishSquish is an arcade-style game where you use the arrow keys to move your character around, avoiding enemy jellyfish and pushing rocks to squish them. You can destroy all enemies to advance to the level -- but as the levels progress, the layout becomes more confined and your enemies will move faster. The game has an educational element: if you push two rocks together, they combine into one rock with the two numbers added, and if you can add up to 15, you get a bonus that stuns your enemies.
I developed this game for the One Laptop Per Child XO laptop as part of a game jam at my college. It also runs on Windows, and is quite portable due to being written in PyGame.
It's inspired by an old Mac shareware game, but I've added some twists like the educational aspect mentioned above. It has been interesting to use the OLPC hardware and meet with the devs a few times at the Media Lab. The OLPC project is described on Wikipedia here.