Murray Leinster wrote a number of fascinating short stories. One that has caught my interest is Gateway to Elsewhere(Baen) being a story about the nature of dimension travel through what amounts to probability.
The central narrative conflict comes from the choices and shaping of environment around the protagonist by two supporting pseudo-characters: a coin manufactured in an alternate dimension and the protagonist's quite vocal conscience imparted by a "maiden aunt who raised him."
From a RPG perspective, the conflict is between the ability of these two forces to manipulate the protagonist's environment such that he (in the coin's view) can return the coin to its native dimension and (in the conscience's view) behave like a proper young executive in the 1950's milieu.
This question in many ways inverts the traditional RPG, providing a requirement of multiple GM-conflict with a sole PC. Therefore, is there a system that allows for players to act as world-shaping entities like a coin or conscience that impact the GM's narration of a protagonist or a system that more directly provides for multiple conflicting GMs and a single PC?