PySide is described as 'The PySide project provides LGPL-licensed Python bindings for the Qt cross-platform application and UI framework. PySide Qt bindings allow both free open source and proprietary software development and ultimately aim to support all of the platforms as Qt itself' and is an app in the Development category. There are more than 10 alternatives to PySide for a variety of platforms, including Linux, Windows, Mac, BSD and Android. The best alternative is Qt, which is both free and Open Source. Other great apps like PySide are GTK+ (Free, Open Source), wxWidgets (Free, Open Source), Avalonia (Free, Open Source) and Uno Platform (Free, Open Source).
Nana C++ Library takes aim at easy-to-use and portable library, it provides a GUI framework and threads for easy programming with modern C++ methods, such as traits, metaprogramming and other template technologies. http://sourceforge.net/p/nanapro/blog
Crazy Eddie's GUI (CEGUI) system is a graphical user interface C++ library. It was designed particularly for the needs of video games, but the library is usable for non-game tasks, such as applications and tools.