To make music sharing more interactive, Ljung and Wahlforss created tools that plug into every social network and allow commenting on specific parts of tracks instead of whole songs. Now some of the biggest acts are super-users and innovators on SoundCloud. Here, the three most socially dynamic:

50 Cent
Ljung: "Last year, 50 posted a track where he is just rapping, telling everyone to produce around that. That blew up in a couple of hours. People were so creative, making a ton of beats."

Foo Fighters
Wahlforss: "For Valentine's Day, they made it possible to dedicate one of their songs to anybody on Facebook and record a dedication, so it played with the song."

Imogen Heap
Ljung: "She's so connected with her audience. She made a track by just asking people to submit snippets of sound. Once it was published, she linked to all the different sounds so that everybody got to be part of what she was making."

See more Social Mavericks