Recording exchange. Here's how I envision it. You pop onto this website, and visit different catagories. Rock Jazz Funk Noise/Strange Reggae Punk Blues Whatever. Anyway, you go to your genre, then you find what the track needs/already has. So, you select Reggae. OK, this Reggae song has drums and guitar, but it needs bass and vocals. So you could work on it, and add bass, then upload it, and show it to the person who submitted the original. They can decided at this point, "OK, we've got bass" or if your bass isn't what they were looking for, scrap it. I know there are issues with copyrighting, etc. But musicians would have to be willing to go uncredited, unless the person isn't a jerk. Like if someone needed bass for an album, and you finished off their song for them. They could either go ahead and say they did the bass, or they could credit you. But you couldn't sue. It sucks, but that would create a mess of paper work. You should have to agree to an online waiver of your rights to "own" your performance. This might not be popular, but I think it would be fun, just to mess around.