Atomverse
This is not a single world, but a universe created by an extinct civilization of post-human´s race. Trillions of trillions of years of order and prosperity were enough to create a massive structure that connected all the worlds without life by magnetic pillars, while the planets with life kept flying around the structure: The Atomverse.
A civil war inside this universal empire destroyed and irradiated the civilization, extinguishing most of the alien life and leaving just a few earth animals to evolve in dead worlds.
This proyect is made to create a saga of books and series, but if you want to make it a campaign it´s ok.