[lunatic]

Not actually a small Unix shop from the 80s and 90s, but Sony produced a line of machines called "NeWS", as in "Net Work Station". As far as I remember the origin was to create a workstation for the Japanese market that was close to, but not really, a VAX. Early machines were 68k based, later ones MIPS based. The OS was called "NEWS-OS" and was a pretty straight 4.3BSD in the beginning. They later switched to a SVR4 style system that I have never seen personally.

https://en.wikipedia.org/wiki/Sony_NEWS

https://kb.pocnet.net/wiki/Sony_NEWS-OS_3.3

https://www.youtube.com/watch?v=d3V1fbKTlyY


Aside from that:
MIPS Risc/os: the thing that IRIX was based on in its early stages. It was also cloned onto a few even rarer machines.
Siemens SINIX: a strange System V based system that ran on a range of very proprietary NSC32k, x86, and MIPS based systems.
Motorola System V: this eventually evolved into a SVR4. They had 68k and later 88k ports. I think the later PowerPC machines all ran AIX.


If you just want something to play with, might I recommend Ultrix?

https://en.wikipedia.org/wiki/Ultrix
http://gunkies.org/wiki/ULTRIX

It is very easy to run this on an emulated VAX (simh). If you want to be truly badass, go for ULTRIX 3.0 and enjoy all the bugs and horrors of a 1980s UNIX.