I've used a lot of, "Collaborative homebrew based on published work".
In several campaigns (not D&D), the game was written with an implicit setting, but they were more "adventure seed" settings, rather than the well-developed canon settings that D&D players working with, say, the Forgotten Realms or Eberron are used to.
In one I ran a couple years ago, and another I'm playing in now, the entire campaign has run in a 50 mile radius of its starting point. There is theoretically a larger setting, but it exists only as a frame to lay some assumptions, like "dragonborn exist" and "there is a large city to the north from which trade flows". I am hesitant to really say those are "in a published setting" given how little of the setting actually appears or is even referenced in game.
Basically, this thread brings up the question: What does it mean to "use" a setting?