Model UN is an extracurricular activity that enacts UN-like sessions with high school students. Each school is assigned a country, and the students involved are delegates for different committees from that country, much like the real United Nations. Each student researches their country's policies (this can be quite difficult to do if you get, say, Romania) on various things. They then attempt to model those policies in this committee environment.
For me, Model UN was a good taste of the flaws of democracy and committees. In my senior year of high school, I was the delegate for North Korea (ok, the People's Democratic Republic of Korea), on the International Atomic Energy Agency (IAEA) committee. Just one week before the session was to occur, North Korea was involved in an incident where they were suspected of possessing the Bomb. I had a lot of fun - I tripped delegates up on their research, I stopped progress from being made, I argued against things and then for them. The only resolution passed was one with a huge hole in it for "my people" to manipulate.
All in all, a ton of fun.