I had written a similar comment here asking for people's opinion but I would like to add something that I know about which I didn't see in your list
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?
Tinycore's package format sounds a lot like containers, except I imagine containers can do a whole lot more, what with namespaces and all. Can't say for sure, but it sounds like snap and flatpak are its spiritual successors.
For that matter, if we're including the proprietary OSs, HP-UX is still kinda a thing and AIX is going strong. Of course, IIRC those are actual certified UNIX™ instead of unix-like... though I'd call that a subset, so still in scope IMO.
I use that one for image gen too. Ask for a picture of a grandfather clock at a specific time. Most are completely unable. Clocks are always 10:20 because that's the most photogenic time used in most stock photos.
https://guix.gnu.org/manual/devel/en/html_node/Invoking-guix...
reply