Question: I was wondering it for a long time since Apple released iTunes for Windows. What did they use to write iTunes for Windows? It seems completely with its own UI components and everything is contained inside it. It even uses QuickTime resources files. Can we assume that they've Cocoa working with windows. Anyway, my main question is, is there any known (public or private) tool/language/framework used in developing iTunes for Windows?

Answer: 
Not a direct answer, but if the reason you're asking is that you want to port a cocoa application to Windows, you might be interested in this:

<http://code.google.com/p/cocotron/>

bit more info here:  

<http://cocoawithlove.com/2010/04/design-of-multi-platform-app-using.html>  

<http://cocoawithlove.com/2010/04/porting-mac-program-to-windows-using.html>

Haven't used it myself, but I gather they've got enough done to make a useable cross-platform Cocoa app.
itunes for both mac and windows are written in c++ as it is easier to port between operating systems with much or the same codebase