Mercora is a new P2P application that allows users to share songs without actually downloading them. The files on your computer are streamed over the net allowing users to listen.
Started by a former McAfee CEO, Mercora has acquired licenses to allow the legal use of this technology. Likewise, it also shares pictures, and videos will be shared soon.
One of the coolest features is the integrated instant messenger. It integrates the media streaming into chat which has extreme potential. Hopefully Mercora can survive against the RIAA and the DMCA.
Check it out: http://www.mercora.com
Mercora allows you to open any song on your computer, and while playing it, have it broadcasted so that users looking through a list can search for a certain artist or member and begin listening to the song off your computer, though, like a radio, they cannot download the song.