Well I dunno how unique mine are but I'll give some short snippet of the one I am working on right now:
It is set on a infinate plane which is the last refuge of a once powerful multiverse. All the people's of the verse settled here, refuges from their homes taken from them by what is simply called the Blackness.
The Blackness is actually the beginnings of a new multiverse that began to form out of the growing distances between the verses. It slowly began to eat away at and destroy the old verse, the "Blackness" is simply the border of this verse.
For a short while the refuges of the planes peacefully began to colonize this last seemingly impenetrable plane. Then the Blackness came, it came in the form of a seething and boiling darkness blocking out the sky. Chaos erupted and severed the fragile peace; war, genocide, cults to the Blackness all formed in this chaos.
Now a few years has passed and a uneasy truce has been passed across the various points of colonization. Now is a time of discovery, reconciliation, revenge and most of all seeking knowledge of the Blackness.
It is a setting where:
- All manner of race and creature from across every plane converge together in single cities, towns and across this whole plane.
- Advance science, magick and supernatural knowledge left-over from the old verse combine to forge new lives. Cities made entirely of rusted out Astral Skiffs, monolithic skyscrapers kept aloft with science and eldritch knowledge.
- A land of odd and unusual sights; the Blackness above with its tendrils and tentacles weaving down and seeping clean whatever it touches. Great cities plowing along the plains on a wave of tentacles coming from below and not above. A horizon stretching on forever with blackness above and only sliver of red light during the day and the waning moon at night.
- Conspiracy and treason are a daily afare. Many people believing each night is their last. Border conflicts, nights of carnal pleasure and murder mix with desperate delving into archives and gleaming the minds of those of old for a way to stop this doom.
- Once mighty Mega-Cabals of the verse now send research times to explore and understand this new universe, and perhaps work with the denizens that lay within.
- The mysterious changes in the plane, could the Blackness be seeping in, in other ways.
So yeah, that only scratches the surface really. It is mainly oriented around figuring out what the hell the Blackness is (PCs don't know it is a new universe), figuring out what the corporations are up to, exploring the new plane and deciding whether it is better to fight to survive or enjoy what may be your last days. Plus just cool looking places.