After a conversation with a friend yesterday, I got suddenly curious about a general category of TTRPGs I'm not sure I have a convenient label for other than what I assume is the granddaddy of them all, Gamma World - games set in weird science-fantasy worlds far in the future and/or after some manner of apocalypses, filled with all kinds of mutants, psychics, robots, maybe aliens, strange technologies, and probably more than their fair share of strange playable nonhumans.

Some examples (besides GW itself) would be things like Vaults of Vaarn, Cloud Empress, and The Electrum Archive; at a stretch you could probably also include things like The Wildsea and Songs for the Dusk, and in other media this would be video games like Caves of Qud, Nuclear Throne, maybe Fallout, or the Ghibli movie Nausicaä of the Valley of the Wind.

Anything else that I've missed?

Vaarn 2e is almost done and Plasmodics is coming out soon!

Mutant Crawl Classics is likely the closest modern simulacrum.

Ashes Without Number is a post-apocalypse game, part of the "Stars/Cities/worlds Witout Number" series. The basic version is free on DriveThruRPG.

You are missing Mutant Crawl Classics. It's literally Gamma World using the DCC framework.

Numenara if it's not been mentioned.

I think Eco Mofos, Lost Eons, and Islands of Weirdhope would all fit in this category?

Breath of the Wild sounds like it would count.

Rifts and Deadlands: The Wasted West could both fit.

Godbound is a neat postapoc setting. Humanity achieved post scarcity levels of abundance, all questions have been answered, with the only thing remaining - which philosophy is right? So humanity decided to go ask the ultimate authority - the creator god of the universe. They stormed the gates of heaven and entered their throne room, only to find it empty. Well, if they couldn't figure out who is right, they will settle for who is left. They stripped heaven for parts to build their own Made Gods and waged a war so devastating it broke reality. The angels were also so pissed at humanity for ruining everything that they turned the machines of reincarnation into hell to torment the souls of the dead forever.

Not sure if Tekumel/Empire of the Petal Throne exactly fits, but figured it was worth mentioning:
https://www.tekumel.com/about.html

* Ultraviolet Grasslands
* Apocalypse World
* Mutant Year Zero
* d20 Modern's d20 Apocalypse sourcebook
* Mutant Epoch
* After the Bomb
* Other Dust
* Fragged Empire

Honorable mention to Masters of Umdaar, which is very much in the He-Man/Thundarr vein, though not exactly post-apocalyptic.

Troika

Do we really need to shout out the work of a Neo-Nazi?

Author's beliefs aside, Tekumel is VEEERY dated anyway