Mac OS 1 through 9 == junk.
Early mac were slightly lacking. But not junk.
Mac OS 1-7 were what they were - revolutionary for the time, but designed for 80s microcomputer hardware. Crucially, they didn't offer true pre-emptive multitasking or multi-user facilities (Multifinder and System 7 multi-tasking was "collaborative" i.e. relied on tasks regularly handing control back to the OS).
It all went runny with Mac OS 8.
Mac OS 8 was
supposed to be an all-new, modern OS codenamed
Copeland - but that project turned into a horror story that software developers tell their children at night if they want them to grow up to be chicken farmers. So MacOS 8 and MacOS 9 were warmed-over versions of System 7 with some multitasking kludged in & were way past their sell-by date.
At the time, the only user-level OS that was better than Classic Mac OS (up to and including 9) was AmigaDOS.
Yup, Amiga was something else. I think AmigaOS was the first OS to offer preemptive multitasking on a mass-market personal computer (not counting Unix workstations that cost as much as a small house)... Not sure it had Mac-level UI design, though. There was also Acorn RISC-OS which offered some interesting UI features (like pre-TruType anti-aliased, outline fonts) and, of course, ran like the clappers on ARM, but that was a bit kludgey - and single-tasking - under the hood (again, a lash-up introduced when an ambitious, next-generation OS project failed).
Well, not really. Back in the early 1970s there was briefly a distinct operating system called Unix that quickly schismed into System V and BSD and continued to fragment, until "Unix" became a set of standards & design principles linked to a licensable brand name.
Paradoxically, MacOS 10+
is Unix and Linux
is not Unix - in fact it uses the GNU toolchain and userland and GNU stands for "GNU is not Unix"!
Considering that MacOS is by far the best known product on that list outside of commercial niche, it's tempting to say that Unix
became MacOS.
...of course that's purely because getting Linux certified as Unix(tm) doesn't sit well with Linux's "copyleft" open source license.
NextStep/MacOS X is BSD userland on top of a modified Mach kernel as opposed to a traditional UNIX kernel, somewhat the same way QNX has a UNIX compatible userland with a micro-kernel. This doesn't make MacOS X or QNX bad, but they are subtly different than traditional UNIX.
I think the idea of a "traditional UNIX" has passed into history - it's been pick'n'mix with a multitude of kernels (monolithic, micro, hybrid) and at least 3 "userlands" (SysV, BSD, GNU) and different "init" systems.
Really, the interesting thing about NextStep is not whether or not it is Unix (if Apple had wanted Unix they already had
A/UX) but that it had a proprietary and very forward-looking object oriented application framework and Postscipt-based GUI that is nothing like the various X Window-descended UIs seen on "traditional" Unix & Linux. That's why half the library functions in MacOS still start with "NS"...
ISTR MacOS wasn't registered as "Unix" until about Tiger, and, before that, the "BSD Subsystem" that gave you the "traditional" Unix tools and terminal was an optionsl add-on.