I'm planning on designing a custom OS X app entirely via Axure and am in the process of creating my own set of custom widgets to prototype and spec an OS X-centric UI.
I'm not completely done but almost there. If anyone is interested, I'm open to open sourcing my widgets once the project is done.
I've attached an early mockup of the widgets so far. The only bitmaps used were the TextEdit component and the search field icon. The rest are all generated using Axure's built-in vector tools. The symbols (arrows and checks) are Dingbat fonts and the system font is Lucinda Sans, which is similar but not exactly the same as the Mac's Lucinda Grande font but good enough for these purposes.
Thoughts?
Disclaimer: I am not an employee of Axure nor am I compensated by the company in any way, shape or form. Rather, I have a vested interest in its continued development as an avid user of the application on a daily-basis.