When I started thinking for last week's post the obvious example of what to do with multiple endings based on decisions by the audience are the Choose Your Own Adventure books. Up the level of interactivity are the pseudo-role-playing games where the reader makes their choices but also uses dice/game mechanics to further decide outcomes and add layers and flavours to the narrative. Then of course there are the ultimate user choice narratives, role-playing games themselves.
These aren't the only options if choices made solely by the author are considered as well. There are alternate history novels as one example. Time travel stories are another branch of this type of story. Multiple character choices and decisions are examined and the outcomes are all laid out often over large temporal stretches to really get at how things have been changed by a particular event's outcomes.
Time travel isn't the only way to do this. The TV show Sliders is a fine example of examining how small changes may have large impacts on characters and the larger world at hand. It lacked a certain level of interaction between different universe's versions of the same character, though it did dabble in it a bit.
When I first set out to talk about this I imagined more ambitious uses of this idea. An example might be a series of books with an ensemble cast--the same basic characters playing different roles--where each book exists in a different world, but they begin to mingle and interact at some level. The first problem to tackle in plotting something of this sort is to not to tell stories that are too similar, yet have the commonality to really compare and contrast the character of these characters as well as the events portrayed in each story. Of course it also requires deciding what the interaction of these characters and worlds is all about and how to pull it off. As I said, an ambitious idea, and fraught with as many difficulties as it may have detractors. There are of course less ambitious takes and simpler approaches, but why not think big first then work down to feasible.
Music: Homecoming by Green Day and Saints of Los Angeles by Motley Crue.