Troupe play is a specific style where the group is encouraged to collaborate in creating and running the game. There's often more than one GM, players often run more than one character and, indeed, there may be a "pool" of characters which they share.
More details on Wikipedia.
I first encountered this in the game Ars Magica and that Wikipedia article says that's where it originated, which was also my understanding. It also says it is used in some other games, where it is called "collaborative role-playing". I've seen that claim made elsewhere.
However, I can't recall ever having encountered another game which even suggested this approach to play, let alone made it a central feature as Ars Magica does.
So: what other systems have been influenced by Ars Magica to include elements of troupe-style play?