Re: Who invented what?
"The first GUI driven desktop operating system? Nope. Not in-house. Licensed from Xerox."
It wasn't licensed. It was loosely copied based on what they could see at a Xerox tour. They may have poached some Xerox people later. Xerox, stupidly, went after Apple when Apple sued MS for copying Apple (at a much later stage). Xerox wasn't in the OS arena, and didn't really know what to do with it's ground breaking GUI tech.
Xerox themselves created their system inspired by Douglas Engelbart's NLS (from 1968!).
"The much loved OSX. Nope. Re-written on top of the Open Source operating system, BSD."
OS X is a UNIX-type system based on Next STEP, which was indeed partly based on BSD but with a Mach OS kernel. There are many such BSD derived systems. It has had extensive changes, and the graphics subsystem is unrelated to other Unix systems.