It didn't get 'incorporated'.

OSX/macOS/iOS is the latest evolution of NeXTStep/Mach which originated in the Aleph (and other) academic kernels.

(of course OS's evolve pretty far in a few decades...)

(https://en.wikipedia.org/wiki/Mach_(kernel))

My understanding was always that NeXTSTEP served as the foundation of OS X, and while it certainly got a new desktop environment and compatibility with MacOS's legacy Carbon APIs, it was essentially still NeXTSTEP under the hood.

Yes. That is all those NS... prefix meant.

I always thought that, too.

It's wrong.

Original NeXT classes were prefixed NX_. Then NeXT worked with Sun to make a portable version of the GUI that could run on top of other OSes -- primarily targeting Solaris, of course, but also Windows NT.

That was called OpenStep and it is the source of classes with the prefix NS_ -- standing for Next/Sun.

https://en.wikipedia.org/wiki/OpenStep#History

This is why Sun bought NeXT software vendor Lighthouse, whose CEO Jonathan Schwartz who later became Sun's CEO.

Unfortunately for NeXT (and ultimately for Sun), right after this, Sun changed course and backed Java instead.

> Everything that starts with NS was part of NextStep.

Not quite. Everything in Foundation gets the NS prefix because it's in Foundation; only a fraction of it came directly from NeXT.