interesting: it did appear pretty popular behind the iron curtain (as did e.g., PL/I, home-PC sized PDP11s, and other seemingly well designed but less commercially successful western technologies.)
You can get a modern Unix running under Hercules pretending to be a more modern mainframe if you want it though. Red Hat, SUSE and Canonical have versions for it, as well as FreeBSD and NetBSD, although I don't think there is anyone using those two seriously.
This might be it.