I know that Polish IPIX (not much is known about it tho other than it was written to run on Polish Krak-86 computer https://pl.wikipedia.org/wiki/IPIX) was already POSIX compliant in 1988. I don't know much more about it's age - is it "older" than 1988 or not. History of communist era hardware and software are not part of teaching program in Poland and only few hobbyists seems to care about collecting and keeping software, hardware and documentation from these times as well as recording history of that era of computerization in Poland.
I see no mentions of any other UNIX type OS on x86 platform this much back in time. Only 386BSD that was being developed since 1989 (which makes it younger than Minix and IPIX).
Were there any other notable or obscure attempts or successes in creating "UNIX for x86"?