Swedish interactive design shop, Dinahmoe (responsible for another great Chrome experience), has recently released a mobile version of Plink—an interactive music creation tool that allows you to collaborate and create songs with friends online.
I played with the Chrome-based version, and the interface is simple and intuitive, but it’s somewhat difficult to understand what you are contributing sonically. Excellent concept, however—would love to see this technology applied to a live performance where fans can contribute through their mobile devices.