Qt is defined as a cross platform application. It is a framework which is used in to develop application software. This application software is developed with the help graphical user interface. This cross platform application is also used in developing non graphical user interface programs. Some of the programs which use this application program are Google, Adobe Photoshop, Panasonic, Philips etc.  This application uses the C++ language. But Qt uses a unique code generator with many macros to enhance the language. Qt can also be used in many programming language with the help of language bindings. It is used on many platforms and is also internationally recognised. This cross platform application was developed by Trolltech but they later sold this application to Nokia. The software libraries which use this application are advanced component framework, KDELibs, LibQxt etc.

QT game screen

QT demo application

Qt has always been available through a commercial license which allows the expansion of proprietary purposes without any restriction on licensing. In addition, Qt has been steadily made open through an increasing number of other free licenses. Currently, Qt is accessible under the General Public License (GNU); this provision makes it available for utilization for both free software and proprietary. Before the 1.45 version, the source code used for Qt was published under free Qt license. This was not really viewed as amenable with the free software description of the Free Software Foundation and neither by the Open Source principle as described by the Open Source Initiative. The reason behind this was that it did not allow the distribution of other modified versions.
In 1998, many controversies broke out when it was acknowledged that KDE’s  KDE software compilation would undoubtedly become the leading desktop setting especially for Linux. Owing to the fact that it was founded on a Qt basis, many professionals who took part in the free software movement became apprehensive that an imperative component of one of a leading operating system would become proprietary.
Along with the release of the 2.0 version of the toolbox, the license was transformed to the QPL (Q Public License). QPL was a free software license but it was considered incompatible with GPL by the Free Software Foundation. Trolltech and KDE then sought out many compromises which would imply that Qt will not be regarded by any license more restrictive than QPL, even in the case Trolltech goes bankrupt. This major issue led to the invention of the free Qt foundation by KDE.