plan 9 is absolutely my favorite operating system. some background:
<– the bell. bell labs invented what was really the first multi user operating system, i would say it was the first “real” operating system. it had novel ideas like files, directories (folders), pipes, users, permissions, signals, etc.
this operating system was called UNIX and almost every OS now is a descendant of it. OSX is unix. BSD is unix. IRIX was unix. linux is unix although completely re-implemented from scratch. windows is not unix but might as well be since they copied all of its ideas.
plan 9 is an operating system that was initially written by the same ~4 people (rob, ken, dennis, brian) that wrote unix and is in very many ways a progression from the old ways of thinking about system software, and “feels” like no other operating system i have ever used. a lot of its ideas are, in my opinion, ingenious
plan 9 didn’t do so well, however, and isn’t really officially maintained by the labs anymore. i somewhat associate with a group of people maintaining a fork of it, called 9front
they have a lot of character which is really refreshing to see in software