There was a lot of OS research pre-unix. In some sense, unix, at least the API, killed them.
Lots of folks were working on "portable" (as in "easy to port") OSs at that time but unix won the battle on PDP-11s and the other ISAs failed to gain much traction.
My favorite was OS was Tenex, from parc (?) which later became TOPS-20. (TOPS-10 ran on the same basic hardware but was completely different.) However, it wasn't portable.
Early in my career I was lucky to use Unix System V. I found those voluminous unix manuals so natural. I could find anything came to my mind less than a minute. Unix system was so coherent, so intuitive. I still enjoy unix prompt, shell to this day.
His book "The C Programming Language" has been the best language book I have ever read. So succinct, but so rewarding for those who studied diligently. Such a beautiful book. I always took that thin book as a standard to compare all the technical books I encountered. If it is that fat I thought there must be something wrong with either the book or the subject of it.
In a broader context:
There was this article recently about Steve Jobs. In that it said somewhere around 90 billion passed through this life and only a few could be able to find his/her voice. Many died before his full potential could even be recognized by themselves. I wonder what would world look like if those could fulfill their talent to their maturity. Because not all societies of the past allowed such liberty for many.
VMS was a a reaction to UNIX, I'm not sure how different DEC's operating systems would have looked if UNIX did not exist.
VMS runs on ALPHA and ITANIUM systems, it doesn't run on anything that vaguely qualifies as a PC, unless you think Windows NT is a VMS variant. It's certainly influenced by VMS, but I say it's a different product.
This is a really good question. All operating systems I am familiar with owe their heritage to C and most of them also to Unix. I would like to know too.
Lots of folks were working on "portable" (as in "easy to port") OSs at that time but unix won the battle on PDP-11s and the other ISAs failed to gain much traction.
My favorite was OS was Tenex, from parc (?) which later became TOPS-20. (TOPS-10 ran on the same basic hardware but was completely different.) However, it wasn't portable.