Qt is a rather magnificent and silent framework. Every application I tend to find amusing and well developed, is based on Qt, but nobody really knows that. There's not much boasting around it, as it is around .NET Framework.
As a few examples, VLC, Google Earth, VirtualBox and the whole KDE desktop and all of its applications, are based on Qt. Nowadays Qt provides cross-platform programming for Windows, OS X, Linux, Symbian, Android (beta), Windows Mobile (beta) in a dozen programming languages (C++, Python, Java, Ruby, PHP, etc.).
Compared to GTK it is very well designed and provides for a magnificent quality of code. Unfortunately based language for Qt is C++, which is not really suitable for most of todays applications, since they rarely require that much performance and low level access.
Python on the other hand, is the jewel of high level programming languages. PyQt, is a robust Qt binding for Python, provided by Riverbank Computing. PyQt is installable in Ubuntu linux with just a few apt commands. There is also a stable Windows installer with Qt libraries included. Unfortunately until now there were no OS X binary distros, and compiling PyQt on OS X was a big hassle.
I have a separate post on how to compile the pile on OS X, but no need for that as I have published PyQtX, the binary distributions of PyQt on OS X, which is available both on Riverbank Computing's PyQt download page and sourceforge.net at the following address:
If you live on a Mac OS X, and you are a developer, this is a must have. You need Python 2.7 for this to use (obtain from official website).