Guess Who? with your friends
This was a fun project to build the game Guess Who with your facebook friends, as suggested by a friend of mine.
Facebook doesn't let you directly access profile pictures or other data of people unless they've explicity allowed your app access. Without pictures the game doesn't really work, so I abused the game-invite api to scrape pictures. However, it never really worked outside of developer testing, and facebook's since locked stuff down more.