They mention in the faq that they do not use GNUStep's implementation of the frameworks, but they do use GNUStep's implementation of the libobjc2 runtime. There's licensing and goal issues. Apparently their Cocoa implementation comes from "the same source" as Darling's, but I don't know what that means. (Cross referencing with Darling's faq, I guess it's The Cocotron.)
GNUStep is GPL though, and one of the stated goals of ravynOS is to be BSD and MIT licensed. On the FAQ page they address this, even saying they might be willing to use it despite the licensing.
> If what you understand by macOS is how Panther used to be.
That's a bit old for me (I started with Tiger), but I would definitely be all over an option to go back to OS X (where, I felt, the paradigm was that users should be presented with the best possible default experience, but also should be trusted to tinker if they chose to do so) before they started pushing this macOS = iOS integration (where the paradigm should be that users should be protected, even against themselves, from any need or ability to tinker).
