Wikipedia
wxWidgets (formerly wxWindows) is a widget toolkit and tools library for creating graphical user interfaces (GUIs) for cross-platform applications. wxWidgets enables a program's GUI code to compile and run on several computer platforms with minimal or no code changes. A wide choice of compilers and other tools to use with wxWidgets facilitates development of sophisticated applications. wxWidgets supports a comprehensive range of popular operating systems and graphical libraries, both proprietary and non-proprietary, and is widely deployed in prominent organizations (see text).
The project was started under the name wxWindows in 1992 by Julian Smart at the University of Edinburgh. The project was renamed wxWidgets in 2004 in response to a trademark claim by Microsoft UK.
It is free and open source software, distributed under the terms of the wxWidgets License, which satisfies those who wish to produce for GPL and proprietary software.