Heptarchia is a quickie campaign world I created as an experiment in worldbuilding using the Adventurer rules.
The Fey lived here, and for millenia imported humans as pets and slaves; then the pet humans learned magic and killed almost all of the masters with one big spell (hint: rain of blood) while leaving almost of their KewL Stuff intact; but then the wizard-pets were overthrown by the slave humans , who decided, after consideration, not to just substitute one master for another. Then everything went to hell, and their relatives showed up looking for land and leibenstraum.
Now, seven major tribal states exist on the ruins of the fairy kingdoms, centered on the abandoned Fey cities, which are about 10% populated. Mad max meets Broken Sword meets Corum meets Atlantis, meets volkwandering post Roman Britain. Evil Elves, Trolls with brains, magical experimental monsters set free, pissed-off banished sorcerors a-plotting, ignorant and brutal kings with poorly understood ancient magical technology ruling bronze and late neolithic tech tribesmen(Thamaturgically Elevated Dictatorships for you New Era fans....); Oh yeah !
More to come.