Writing software that works seamlessly on Windows, OS X and linux is made easier with the right tools. Qt is a crossplatform toolkit that allows just that. And Python is a language that is a pleasure to write in. Combine the two and you get PyQt. Unfortunately, Python is only installed by default on linux and OS X, it is a third-party install on Windows. And Qt is only installed by default with KDE-based linux distros. Even worse, PyQt is not available except as source code on OS X (the PyQt3 binary available for OS X is too old to be even remotely relevant) which means an end user has to compile it just to use software written in it.
Neither Microsoft nor Apple has any incentive to provide Qt, much less PyQt, as part of their default install. In fact, they have disincentive to do so as it only weakens the boundaries between operating systems which they rely on for differentiation. Part of the answer to the problem lies in packaging. Instead of providing the Python code and relying on the user to install Python and PyQt as necessary the application can be packaged up as a binary with (almost) all necessary libraries included. On Windows the binary will still require the Microsoft 2008 runtime (which may in fact already be installed on the system). As Microsoft has a habit of rearranging their site to break outside links such as this doing a google search may be more productive.
The software published by Hammurabi Concepts is all written in Python with PyQt where relevant for the user interface.