It may only be a technical collaboration, and there are doubtless hundreds of other collaborators, but I've now been fortunate enough to work with Meg Cabot on a new BBC audiobook.
OK, so maybe it isn't exactly as exciting as it sounds, but it is a load of fun, and anyone with a Twitter account can join in the thrills.
The story unfolds in real time, and (being Twitter-based) contributions are limited to 140 characters at a time. It's engaging, and I found myself hovering over the computer to see what happened next, even when I couldn't think of anything to add.
BBC Audiobooks has a blog recapping the story so far. If you scroll down to the "60 minutes and counting" post there are instructions on how to join in.