Mac OS?
macOS is certified Unix, and necessarily implements the "legacy" cruft.
Tinycorelinux
I know that it doesn't follow the best user practices etc. but I did find its tcz package format fascinating because they kind of work similar to mountable drives and I am not exactly sure but I am fairly certain that a modern package management system where two or more packages with conflicts etc. can run on the same system.
I really enjoyed the idea of gobolinux as well. I haven't played with that but it would be good if some more mainstream os could also implement it. Nix and Guix are more mainstream but they also require to learn a new language and I think that we might need something in the middle like gobo but perhaps more mainstream or adding more ideas / additions perhaps? I would love it if someone can tell me about some projects we are missing to talk about and what they add on the table etc.
I haven't tried Gobo though so I am not sure but I really wish more distros could add features like gobo, perhaps even having a gobofied debian/fedora eh?