UIKit for OS X
UIKit for OS X basically ports UIKit from iPhone to the Mac. You get the great classes you have on the iPhone (UIApplication, UITableView, etc) on the Mac, backed by Mac versions of those classes.
Adding UIKit to your project
UIKit compiles as a native OS X framework. You have two options for including it in your project: do a one-time compile and bundle it with your software, or add it as a dependency to your project to keep up-to-date easily.
More information will be added later on how to do this.