More important than the acronym is the effort itself. XINU is a really interesting project and probably the second OS I was introduced to outside of the POSIXy neighbourhood. It differs from a lot of other projects in that its goals (to my understanding) were very different to the usual approach toward providing POSIX compliance or a platform intended to support layering POSIX on top of a base architecture.

I picked up an old copy of the textbook and never read it. Maybe this is the kick I needed to pick up the newer edition and actually check it out in earnest!