Here's a short, rough version of my idea:
The Four Horsemen of the Apocalypse have been watching over mankind for millennia, growing tired of their slow decay and rising population. So the Four have come up with the idea of a tournament of death. Each will pick a group of humans to fight for them, bring them to a different dimension, kill them and reincarnate them. During their re-birth, they receive powers or skills to use to fight their opponents. Whichever Horseman wins the tournament, they do to the human race whatever they please. War: a war that will kill all humans and no nation stands victorious. Famine: to have every human die slowly of hunger. Pestilence: to plague humans with fatal, incurable diseases. And Death: to enslave the human race, only to slaughter them all in the end.
Anyone interested? Also would it be better as a hosted?
I can see it working good as either way. Seriously though, as hosted I can see it working as a seriously hosted game with a GM. It would have threads for each side and then threads for each conflict e.g one horseman's army verses another's... as unhosted it could work equally well, but perhaps less structured, and the last game I was in that was similar failed miserably. You would have to give a lot of thought into the allowance of powers and such, and maybe only have preset powers to choose from. I dunno...