Originally Posted by
Psychotic
Running with qwerty's idea-
- They are all in the same world at the same time.
- They are all in the same world at different time periods.
- They are all on different planets at the same time (but because they are in different worlds, this can explain why somewhere could be at medieval level, somewhere could be sci-fi, somewhere else could have Elves and Orcs and other fantasy things, etc)
You could still have the same main character for any of these ideas too, with a "he's journeying around the world/universe/through time" thing.