Vladimir Bulatov, Conformal models of hyperbolic geometry.
The chance shirt machine (auf Deutsch).
Foursquare asks: What neighborhood is the ‘East Village’ of San Francisco?, based on what type of establishments people check into in various neighborhoods.
Duels, truels, and game theory gunslinger rules, by David Barash, author of The Survival Game: How Game Theory Explains the Biology of Cooperation and Competition (which I have not read).
Galperin’s billiard method of computing pi, from Calculus VII.
Spiked Math IQ Test. I got a zero. Perhaps knowing this will help you get better than zero.