I work with developers who code on OS 2200 and VAX VMS (running on Charon emulation).

Fun fact: the first SMP UNIX implementation ran on top of EXEC 8, the kernel of OS 2200.

"Any configuration supplied by Sperry, including multiprocessor ones, can run the UNIX system."

https://www.nokia.com/bell-labs/about/dennis-m-ritchie/retro...

Edit: https://web.archive.org/web/20150611114648/https://www.bell-...

https://en.m.wikipedia.org/wiki/UNIVAC_1100/2200_series