So our gaming group has had a few end-of-session conversations about doing some sort of team or collaborative GMing. I remembering trying a variation on the theme back in high school, with a common set of characters flitting from GM setting to GM setting. Each session featured a different GM, using the GM's own setting, but the characters had the (unexplained) ability to move from world to world. I also played in a session in college where the GM tasks rotated from moment to moment during a single session--it was one of the better gaming sessions I have played in, but it was also the only one for me that involved a significant amount of alcohol.
It turns out that Wikipedia, the final arbiter of knowledge in our current age, has an article on this, calling it the Troupe System. Wikipedia summarizes the Troupe System this way: A Troupe system is a way of playing role-playing games which spreads the game master's responsibilities among each of the players. The term was coined in Ars Magica. It is also known as collaborative role-playing, a term used by other games with a similar mechanism.
Thanks to +Chris C. (The Clash of Spear on Shield) for sharing the Wikipedia link with me, as well as a few other links. Here are some other links:
Troupe System (Wikipedia)
Troupe Style GMing and the Gaming Charter (Gnome Stew)
Troupe Style (Project Redcap)
Starting To Collaborate (Collaborative Roleplay)
And my own blog post from yesterday was a lead-in to this post: Microscope and the Books of Bardo