A Qt C++ Library
FlatGUI is an open-source library created to support the development of non-native looking graphical user interfaces for Qt Widgets-based desktop applications. It servers as an extension to the Qt functionality, providing a component development kit (CDK) for the creation of custom widgets, as well as a collection of ready-to-use GUI components.
If you are a die-hard fan of the Qt Widgets technology and QML is not your preferred language, though you still would like to create desktop applications with non-native looking graphical user interfaces, then FlatGUI is made just for you.
For more information, please visit the project page.