This is a little trippy. The band Flaming Lips once released a studio album containing four CDs designed to be played all at the same time. Flaming Lips has upped the ante and uploaded 12 different clips to YouTube, which are all supposed to be played on 12 different smartphones at the same time (or browser windows, if you don't have 12 iPhones). Here's their YouTube account with all of the videos on it, and here's an "instructional" video (beware: the title of the song is not safe for work) detailing how to get the tracks running and sync
