I ran across this video in my RSS feeds, linked over by Gizmodo, and I have to agree with Diaz, "If this video doesn’t bring a tear to your eyes and makes you smile for the rest of the day, you are a cold hearted bastard. Watch it from beginning to end—you won’t regret it."
The basic idea is that they went to Santa Monica, California, and recorded a cover of "Stand By Me" by street musician called Roger Ridley. Then, they travelled around the world with basically a portable studio, adding new tracks with multiple instruments and vocals that were assembled in the final version you are seeing in this video. All done with a simple laptop and some microphones.
Playing For Change, Song Around The World "Stand By Me" from Concord Music Group on Vimeo.