[jwells89]

That's all true, but nonetheless it was a ton of fun for those of us who were into desktop customization at the time. With how system extensions worked in Classic Mac OS (they could overwrite bits of the system in memory) there was practically nothing they couldn't do, and as a result it was one of the most effortlessly extensively customizable desktops to ever exist. Even 22 years later, in some ways Linux, the long reigning champion of customizability, has yet to beat it.

Of course, that extension model was hilariously insecure and wouldn't have worked in the modern era, but it had its perks.

[dansalvato]

This was popular on Amiga as well, although maybe less clean and "officially supported" compared to Mac OS system extensions. There were Amiga utilities that remapped OS system calls to custom functions with performance optimizations, enhanced functionality, or different behavior altogether.

The 68000 series CPUs didn't have an MMU built-in until the 68030, which I guess was far too late to see much use in consumer OSes. Pretty shocking that the jump to PPC wasn't enough for Apple to take care of that stuff, but I guess that was going to be Copland before it was canned. At least Amiga had preemptive multitasking from the beginning.