New open-source framework from Twitter engineers Loren Brichter and Ben Sandofsky:
TwUI brings the philosophy of UIKit to the desktop. It is built on
top of Core Animation, and it borrows interaction ideas from
AppKit. It allows for all the things Mac users expect, including
drag & drop, mouse events, tooltips, Mac-like text selection, and
so on. And, since TwUI isn’t bound by the constraints of an
existing API, developers can experiment with new features like
block-based drawRect and layout.