[anamax]

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.