If you do decide to build this app, I would highly recommend making it open-source. Properly building a custom-skinned OS X app is not easy. Compared to UIKit on iOS, which was built from the ground up to support animation and appearance customization, AppKit is a dinosaur.<p>When subclassing controls, you'll encounter AppKit bugs, things that can't be skinned without overriding private methods, and inconsistencies between OS versions. The animation APIs are woefully inadequate, especially if you need to support 10.7 or 10.6. (over two-thirds of the install base as of January, according to [1])<p>If done well, the source code would be a valuable resource to the Mac developer community. Custom-styled desktop experiences are becoming the new norm, yet building them remains somewhat of a black art.<p>[1] <a href="http://www.cultofmac.com/208455/os-x-mountain-lion-now-accounts-for-32-of-mac-web-traffic/" rel="nofollow">http://www.cultofmac.com/208455/os-x-mountain-lion-now-accou...</a>