I've been lucky enough to participate in The Traveling Quilts bee/round-robin, which is a year-long quilting adventure where each participant starts a quilt then sends it along to the next person (and then the next, and the next after that, etc.) to work on. The last person to get each quilt will finish it for the original quilter.
Unlike a conventional bee or round-robin, where everyone makes roughly the same kind of thing or the same kind of shape, this bee is completely open-ended. Participants are simply inspired by what they get and add stuff accordingly. It is A LOT of fun!