Sorry I am off topic again.
My mention of AIX and HP-ux got me thinking.
I used to use (a little) VMS which became OpenVMS when it was abandoned by DEC.
I have just found that OpenVMS STILL EXISTS !!!!!!!!!???
If you have never heard of it or used it, it was wonderful but very unique to DEC.
Commandline completion was in another world and it would hold your hand and question what you did if it was ambiguous
None of the terminology was like UNIX or Linux or anything else in the world.
But it was 'Rock Solid' it ran and ran and ran. Absolutely Wonderful.
[Sorry, just gobsmacked it still exists.)