A cross platform toolkit for the development of GUI programs. Developed by the Norwegian company Troll Tech. Used in KDE, a desktop environment for UNIX and UNIX like systems. It uses the C plus plus programming language. It runs on all major platforms, and has extensive internationalization support.
Controversy erupted in 1997 (?) when it became clear that KDE was going to become the leading desktop environment for GNU/Linux. Based on the QT Toolkit, which was then under the QPL license, 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 based on code from the GIMP, and uses the C programming language.
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, early 2000 (need exact date) it was announced that the upcoming version of KDE, 2.0 (released at (need exact date)) would be under the GNU General Public License.