Post-apocalyptic settings are numerous in RPGs: here’s a good feature on quite a few of them.
They mostly feature the “fun stuff”: mutants, dungeon crawls, weird tech, a nuclear war, and so on. Something awful happened; the world changed; I need to dress in leather, chains, and old tires, and fight to survive against waves of bloodmurder fuckvikings.
Rebuilding the “world that was” is a central theme to a few of them: The Morrow Project, for example, and in a roundabout way, Traveller: The New Era.
One of the themes I don’t see explored, and wish I could, is the idea of emptiness. How do you build and populate a meaningful game world that is empty, and cold, and lifeless, and barren?
Without the requisite bloodmurder fuckvikings (or whatever) is it just a series of “collect food and clean water” skill checks, until you die? Could all that emptiness be turned into a kind of meta-mystery?