UXKit aims to be an Open Source implementation of Apple's UXKit. Unlike UXKit, which is written in Objective-C and is a private framework only for OS X, UXKit aims to bridge the UI layer between both platforms and provide compatibility at the source code level. Its also written in Swift, which will bring a modern language update to familiar APIs. This means that it goes beyond Apple's UXKit in the sense that you can make custom subclasses of UXView that will compile for both OS X and iOS (for more info on compiling frameworks for iOS and OS X, see this blog post)