Ideas I've had in the past playing a wuxia game using the map of Middle-Earth (and MERP materials), The Known World replaced with Talislanta equivalents, or Creation from Exalted, but built as a D&D setting (using published 5e material).
I've never done any of these as at the end of the day the work required wouldn't be that much less than making up my own stuff in some instances, but it's still an idea that pops up from time to time.
In the game I'm working on, all PCs are defined in part by two Archetypes. These represent types of characters found in comic book Sword & Sorcery. In game terms, they provide bonuses to Attributes and Domains and also special abilities.
Each archetype has a primary and secondary Attribute and Domain. Should a player pick two Archetypes with the same primary Attributes/Domains they can use that one and their choice of the two Archetypes secondary Attributes/Domains. The character also gains the Expertises and Talents of each Archetype.
While the Archetypes remain a work in progress, below is a sampling of the ones I've come up with. At this point, the plan is not to give any description of them beyond the abilities they provide, letting players interpret them as they will.
ACOLYTEAttributes: Presence (Intellect)