If you'd done any amount of Cocoa programming before starting with Cocoa-Touch, your first impression is: how similar these frameworks are.
Your second impression might be "How infuriatingly similar these frameworks are!"
The Nibitaph framework aims to provide, through protocol-oriented programming, a union of AppKit and UIKit that can be used to quickly and easily develop cross-platform (Mac OS X 10.6- and iPad iOS 5.x-) apps.
Home is where the repo is: github.com/genkiyooka/Nibitaph/
Nibitaph is an umbrella consisting of the following submodules: