Qt toolkitThe Qt toolkit is a free cross platform graphical widget toolkit for the development of GUI programs. Developed by the Norwegian company Trolltech. Used in KDE, a desktop environment for UNIX and UNIX like systems. It uses the C++ programming language, but bindings for Python and Perl exist. It runs on all major platforms, and has extensive internationalization support.
Qt now exists in a number of flavours, for various platforms, and these are licensed under various licences.
Qt/Windows - Qt for Microsoft Windows - Proprietary (obsolete version free)
Qt/Embedded (designed for PDAs) - GPL
Controversy erupted around 1997 when it became clear that KDE was going to become one of the leading desktop environments for GNU/Linux. Based on the Qt Toolkit, which was then under the Q Public License (QPL), many people in the open source and free software movements were worried that an essential piece of one of their major operating systems would be under commercial control.
This gave rise to two efforts. First, the Harmony toolkit which sought to duplicate the Qt Toolkit under a free software license. Secondly, the GNOME desktop that was meant to supplant KDE entirely. The GNOME Desktop used the Gtk+ toolkit which was written for the GIMP, and uses mainly the C programming language. Gtk+ attempts to be cross-platform just like Qt.
Compromises were sought between KDE and Troll Tech wherein Qt would not be able to fall under a more restrictive license than the QPL, even if Troll Tech was bought out or went bankrupt. This did not satisfy all the critics, and finally, on September 4, 2000, Troll Tech announced that the upcoming Qt 2.2 release will be licensed under the GPL. Qt 2.2 was released on September 6, 2000, KDE 2.0 followed on October 23, 2000.
Troll tech has subsequently released Qt 3 under the GPL and there is a corresponding KDE 3.x release series.