BSD would like a word.
They can't be heard over the faint booing from the Solaris crowd.
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.
TIL AIX is still in development and they had a release this month
https://community.ibm.com/community/user/blogs/sanket-rathi1...