The main page is here, and if you want a little history on it, read the interview with the creators on Boing Boing. The nicest thing about it is that Songbird is a beginning, not an end. They are making it open and extensible, so if you want to write a plugin, feature or killer app, you can. I expect every P2P network in the world to be compatible in a few days, shortly followed by the non-DRM infected music stores.
With any luck, Songbird will end up as a real music purchasing and sharing tool, a place where you can buy music legally without handcuffing yourself to the wall first. It has great potential, and hopefully a great future. Check it out, and better yet, contribute if you can, code or money, this one is worthy. ยต