BookTenTiger
Sad Dad of the Revolution
Fun idea!
I had two ideas for settings with this concept.
The first I called "Planet Camelot." An alien space ship crash lands on a medieval, Earth. The aliens integrate into society and it creates a sort of Arthurian myth, with aliens taking the place of demons and technology taking place of magic. Merlin is a half-alien who can use psionic powers. The "lady in the lake" is the crashed ship whose artificial intelligence can be bargained with for customized technology (like "magic swords"). The Grail is some sort of technological Macgiffin the aliens need to get home. It's been long enough that the aliens have basically joined medieval society, so you have peasants and blacksmiths with tentacles and knights using a mix of steel blades and alien tech.
The second idea was that aliens colonize a pretty standard D&D world and create these cities that draw thermal energy from inside the planet. They set up their cities on massive towers high above the clouds. The pollutants from their cities creates a constant layer of storm clouds, but that doesn't impact their rosy lives! Down below folks have gathered in makeshift cities surrounding the towers. They draw power by tapping into the cables running up the towers. So the cities are dark from the storm clouds, but neon-lit, with flickering street lights. Everyone wants to be invited up to the cloud cities, so they go out into the world on quests and come back to the towers with their treasures or songs or magic tricks, hoping that they will get a ticket skyward.
