FWIW, my original post referred to "an operating system," which could mean literally any operating system that was developed more than 10 years after 1976.
In context the @Binder post I was replying to, it's reasonable to assume I would be talking about any Linux distro that meets the minimum qualifications of being an "operating system."
For the purposes of the snark, any L i n u x - b a s e d o p e r a t i n g s y s t e m will do, since NONE of them existed in 1976 when Emacs was first designed and released.
So take your pick: Linus' first boot-root distro would work. Or the original MCC, TAMU, or SLS distros. Perhaps the joke works better with Slackware or Debian. Snark doesn't compile for Arch, unfortunately. #IUseMintBTW
Has this horse been sufficiently beaten?