I participated in the make-a-game-in-a-weekend contest Ludum Dare, and submitted this game, which was a lot of fun to make! Ben Rosen did the art, interface and sound, I did the coding for the waves and the sand.
You dig and build to protect your flag from being swept away by the waves.
We'll probably keep working on it a while longer because not everything we planned made it into the submission. At least watching the waves is pretty cool.