On: MacOS Marzipan

[GeekyBear]

When Apple rewrote iPhoto as the Photos application a few years ago, they used a private framework called UXKit that also implements UIKit on the Mac.

They've been working on this for a while.

http://www.idownloadblog.com/2015/02/05/photos-mac-uxkit/

[saagarjha → GeekyBear]

It doesn't implement UIKit; it provides a shim on top of AppKit that makes the API look similar to UIKit.

[tinus_hn → GeekyBear]

Apple always had UIKit working on the Mac, the iOS device emulator runs it.