As an X-Plane user and a Mac developer I have to take my hat off to “Austin Meyer”, the author of X-Plane for one major aspect. I do not know exactly what development environment he uses but the program is absolutely massive. My upgrade last night included over 41,000 files. To top that off X-Plane runs exactly the same on OS X, Windows and Linux.
I have no idea how he does it but I think he must have developed his own, entirely proprietary GUI that does not depend on any specific platform. All I know is it is one phenomenal piece of software and it works as advertised across three different platforms. The man is a genius in every sense. Sort of like the Affinity Team.