Urchin, a single player mini-non-game...thing... is available for free download. Currently it's OS X only, although in the near future a PC version will be released.
Urchin is an interactive program for Mac with a kind of ambient game
mechanics. This minimalist game is small in scope with only about 30
minutes of gameplay. Move your urchin around using the arrow keys to
eat the algae (phytoplankton) with its circular mouth. Through eating
more algae your urchinesque thing will accrue layers. After eating
enough algae you will enter a new phase of music and your urchin will
change shape. The only threat is a jelly fish which is very benign, and
there is no way to win. This 'game' is more about an audio visual
environment and experience.
Currently it is only for OS X 10.4 or
higher but there will likely be a PC port in the near future. The
visual part of Urchin was developed using the Processing programming
environment. The audio was created with the SuperCollider audio
programming environment. Urchin is open source.