The "addventure" is a form of non-linear collaborative fiction that has evolved since the term was first coined by Allen Firstenberg in 1987-88. Primarily a combination of select aspects from both the round-robin style of collaborative, chain-tied fiction with the "Choose Your Own Adventure" method of interactive, non-linear fiction, the addventure is meant to allow for the creation of multiple reality sequences, with authors able to start again from any previous landmark and fork off with their own derivative sequence of following events. 

So while you already have round-robin webcomics and interactive "CYOA" webcomics being published, I wonder if a "addventure webcomic" has been tried yet.

I see such a webcomic as being potentially bigger, more diverse and more rich with parallel dimensions than anything that could be mustered by Marvel Comics.