20 years ago, Trolltech, the company that created Qt, was founded. One of its founding principles was to release Qt as free software to the open source community. In the early versions, this was limited to Unix/Linux and the X11 windowing system. Over the years, more and more platforms were included into the open source version of Qt.
At the same time, the licenses under which Qt was available evolved. The Qt 1.x source code was still released under a rather restrictive license. With Qt 2, we moved over to the QPL. Some years later, with Qt 4.0, Qt started to embrace the GPL v2, to remove some license conflicts between GPL-based applications and the QPL.
Trolltech was involved in talks with the Free Software Foundation (FSF) when the GPL v3 was created, and we added this license as an optional license for Qt after it was published by the FSF. Finally, in 2009 Nokia added LGPL v2.1 as a licensing option to Qt.
The spirit of all GNU licenses is about a strong copyleft, giving users rather strong access and rights to the source code of application and libraries. It was always meant to protect the users’ freedom to modify the application and underlying libraries and run the modified application.