Then there are lots of nits with lots of variants of 'Unix'.
Two variants of Unix I worked with (apart from the RT/AIX VM) both qualify as oddball - these were MACH & AIX/1 on the 370 with its shared file system that ran on PS/2s - that was really oddball & eventually got squashed.
Most people (unix fans) probably know something about Rick Rashid's (CMU) Mach but the 2nd one (370 based) was from one of the other major universities & was originally desined for DG & DEC computers. It allowed a cluster of computers (Servers & Workstations) to look like a single large clustered file system where the parent directory was on the main server each node added a sub-directory which was located on a workstation node. A cluster of 20 or so PS/2s would look like a single large computer. Problems did occur when nodes decided to depart as their filesystem would dissapear so strange things could happen if that cluster node's filesystem was in use.
Re XENIX - I really enjoyed working on Bill Gates version of that - MS had licensed it to ALTOS Corp who ran it on their ACS-x86 family of intel based computers in 1982 which was when I first worked with it. XENIX was so far out in front of other System 7 versions of Unix of the day - Xenix incorporated Bill Joy's infamous Berkeley Enhancements & it was these that gave Unix any commercial power - pure Unix lacked too much that was needed for commercial usage. VI & Termcap, for example, were two features that made a difference. Whilst people can crit VI all they like, the power it brought was that any dumb ascii terminal could be configured in termcap so that an application like VI (and also RM Cobol, MS Basic, etc: - critical to commercial usage) could run without hard coded escape sequences to the terminal. Prior to VI Termcap hard coding to one brand of ascii terminal was the only way to do screen control.
XENIX led the way for many years, as the Unix OS of choice where systems were being placed in real world businesses - Most Universities never understood this & stuck to either UCB or pure AT&T variants (BSD & AT&T Sys III & Sys V).
DSM