O-Mopsi
O-Mopsi is a location based orienteering game. Be faster and smarter than the other players. The world is your playground!
Anybody can use the O-Mopsi website to create a game in their surroundings. http://cs.uef.fi/o-mopsi.
Note that continued use of GPS running in the background can dramatically decrease battery life, especially if a game is started.