Ah, yes, good old A/UX. I remember taking half a day to reinstall it on a Mac II from a box of floppies, staring at the counting fingers on the screen while waiting for the instructions to swap disks.
Only later did I realize how odd it was that they had me doing that on a Mac. Those where the days where they had farms of various Unix workstations because they ported SQL Server to a ton of different platforms. I remember ending up in a storage room one day and there were piles of unopened Suns, Apollos, DECs, SGIs...
Slightly less of a commitment, there was also MPW, which was kind of unix-ish.
https://en.wikipedia.org/wiki/Macintosh_Programmer%27s_Works...