AI Challenge is an interesting, Google-sponsored multi-agent systems contest, that looks a lot like a competition held for a course I followed last year. Up to 8 teams of ants are pitted against each other on random maps, and have to explore, gather food and must plan and cooperate intelligently to defeat their rivals.
I was really compelled to join the competition, but rather late to discover it. Moreover, I was just too busy with other work. Maybe next time!