Hi, we completely rewrite the UIKit framework from the ground up. We started from the abandoned Chameleon Project (http://chameleonproject.org) several years ago and we added tons of classes and improvements in order to be in sync with the latest iOS versions from Apple.

We are able to execute most of the native iOS code directly on Mac, from example this project works without a single code change on MacOS: https://github.com/chrismiles/CMUnistrokeGestureRecognizer (so we have UIView, UIViewController, UIGestureRecognizer, UITouch, UIBezierPath and much much more).

We also didn't block any customisations (like the custom collection view layouts). We simply need more time in order to correctly expose all the functionalities from a graphical user interface and in a coherent way for all the users.