There used to be things like this on Apple's website, too: https://www.apple.com/media/us/osx/2012/docs/OSX_for_UNIX_Us...
I can't find any mention of UNIX in Big Sur's pages, even though it is listed as certified on the Open Group's website.
Newer filesystems and application designs have eliminated many of the differences, although I still miss resource forks.
So the library deciding how to load and possibly when to evict sounds like it was kind of the point. Simulating what might be the job of mmap() on a modern system.
My understanding is that's where file tags, file comments and custom file icons are stored.
NTFS also has multiple forks, and also has many of the same fancy attributes capabilities that made the BeOS filesystem (in)famous, but they're not used in the same way, so it's kind of moot.
What really what made BeOS and Mac OS good was not so much the technical underpinnings, but the way they exposed these in the APIs and standard applications.
The power of Unix isn't just from the presence of the standard I/O routines, but the fact that most programmes are written to adhere to a specific paradigm that allow them to work together.
That said, I think metadata about a file outside of the file has always been problematic. I don't know if there's ever been a clean solution to timestamps, r/w/x, ACLs and more.
That is not true. The desktop metaphor, for example, was first introduced at Xerox PARC in 1970, and used commercially in the Xerox Star workstation in 1981.
Not to mention the OS X-like variants for their other platforms: iOS, tvOS, iPadOS, watchOS...
Also consider the various Mach implementations on Apple hardware: MacMach, MachTen, MkLinux, OS X/Darwin...
Sadly it seems that the classic Mac API died when Carbon and 32-bit apps died, so you can't easily port old Mac apps to modern macOS. macOS (and iOS) seem to have a rather poor record for backward compatibility, and it's only going to get worse with the current architectural switch to Apple Silicon...
