f13.net

http://www.experimentalgameplay.com/

The Experimental Gameplay Project: create 50 to 100 games in 1 semester. New games every week.

The Rules:

• each game must be made in less than 7 days
• each game must be made by one person, including all art, sound, and programming
• each game must be based around a certain "toy" ie. "gravity", "vegetation", "swarm behavior", etc.

The games aren't likely to keep you entertained for more than a few minutes each, but they are all fairly unique.  I particularly like "Attack of the Killer Swarm."