I will make a more formalized write-up if I get interest, but here's the rough version: the more-or-less Biblical Apocalypse happened a decade or so ago, Heaven and He'll went to war over Earth, and 99.9% of the human race was wiped out. You have three factions, scrabbling over what is left of Earth. There are the remnants of the armies of Heaven and Hell, and caught between them are the remaining 0.1% of the human population. Normal humans can no longer survive on Earth; those that remained have been "touched" by an alternate Plane, be it Heaven, Hell, an elemental Plane, etc.
That's basically the gist of it. I'm willing to give liberties with Planes and the powers they give, as well as the powers held by angels and demons. Any takers?