In a nutshell they connect musicians from around the world through sophisticated technology (e.g. enabling a blue guitarist from Mississippi to play with a cellist from Moscow). They also try to spread music throughout the world by donating musical education resources to various communities around the world. Check out the interview with the producer Bill Moyer on PBS's site, it's very interesting. They also have a full documentary you can check out (I haven't yet, but definitely want to look into it). Check out their website (the link up top).
Here's an awesome clip of a collabortation they did for "Stand By Me". Enjoy!