One thing a bunch of us did on another forum I used to frequent was this:
-A forum member volunteers to initiate a tune.
-They select a tempo and key, and produce one track, be it vocal, instrument, drum section, whatever. They put this track on the main thread in wav form.
-Other forum members that wish to participate each produce one more track, and submit it to the lead on that tune, in wav form.
-The lead forum member arranges the tracks, adding their own as necessary to fill out the final track. They have full autonomy on the track's form. The only restriction is that they must use every submitted track.
-When the final tune is completed, name nominations are submitted and voted on.
The tunes that resulted were always really... interesting. Actually, they were quite good, with the nature of their creation taken into account. Our stuff was always more experimental sounding because our frequent contributors made Trance (me), Rockatronic/Nu-Metal? (Actually this guy was all over the place in terms of stuff he made), Post Rock, and Glitch, with random contributions by other members of the community. The names are also really wacky, because we were all really weird experimental dudes.
We may have had a limit of like, six or seven submissions per wave, so it was usually first submit, first in.
These are the tunes we made, if you want to hear the typical result of this kinda thing:
Atom SmasherFourth Song (Rasta Rasta)Haunted Neon LightsTea Time in TijuanaThe Progression of Moments in the Wake of the Big BangThis whole format was really an outgrowth of the fact that one guy used Logic, I used Fruity Loops, one guy used Audacity, and one guy used, like, Garageband or something, since all of his stuff was recorded live.