A/UX was released for the Mac II in 1988, then in 1993 Apple changed course with a series of servers, before Mac OS X Server in 1999 and its first Xserves in 2002.
A/UX
An extended tutorial-review of Mountain Lion Server, OS X Server 2.2, written in 2012-13, with copious screenshots.
Whilst not exactly a lemon, it was not the flagship product which it could have become, and only made it to version 3.
The Eclectic Light Company 