Neverwinter Nights custom servers do exactly this! DMs are always there causing changes to the world based on what players do and organizing all the twists etc.

Neverwinter Nights custom servers do exactly this! DMs are always there causing changes to the world based on what players do and organizing all the twists etc. And on top of that, in the one I'm following at the moment, the world is being eaten by a void and the rumor is that when everything is gone that's gonna be the end forever