InstantAction have announced Instant Jam, a rhythm-based, browser-based, guitar-based, jam-based, gaming-based game. It's Guitar Hero in a browser, it'll let you play with most of your music collection, and it seems to have some sort of dark coupling with the Face Books going on.
Instant Jam works with your keyboard or a USB guitar. It scans your "music library" (which might be your hard drive?) or lets you purchase music on Amazon or iTunes. When you complete a track, you earn 'fans', which go towards gaining levels. Sadly, it doesn't do some sort of Audiosurf-esque magic that analyses your tracks, it just tries to match it to a pre-prepared note chart. The admission is on their FAQ : "We cannot guarantee that every song will have a Note Chart, but we are adding new songs daily. Check back often."
You've got a limited number of "plays" that you can use up. They regenerate over time, your friends can give them to you as gifts, and you can buy them with Instant Jam fake money. It's in beta now, but I can't seem to get in - maybe it's a closed beta? Maybe I haven't clicked enough Like buttons? You can have a poke around on their facebook page , and the official site is here .