foomanchoo
Every song or loop is stored as plain JSON, see the sample beat: https://github.com/Marak/JSONloops/blob/master/loops/nyc.jso...
Each node.js "server" acts as a hosting point for the loop. Any number of browsers can act as a control interface for a "server". Eventually, each node.js "server" will sync up peer to peer.
Audio playback currently occurs only on the "server", but as browser libraries such as http://www.schillmania.com/projects/soundmanager2/ improve, the browsers will also have audio playback.
JSONloops isn't perfect right now by any means, but after checking the commit log from the weekend: https://github.com/Marak/JSONloops/commits/master ( and laughing at the drunken commit messages ), I was thoroughly impressed with how much they pulled off in a 24 hour hacking period
I'm excited to see where this goes.