QT 4 Authorization-for a later version of QT 4.5

The provision of QT products is a dual licensed software licensing model. In this dual licensing mode, QT products can be developed not only for proprietary software under commercial license, but also for free and open source software under the GPL (general Public License, version 2 or version 3). In other words, the QT software itself is open source and free to use, if you are based on the GPL protocol to develop the software, you develop the things will be published under the GPL-open source and provide free source code.

Since the release of Qt4.5, QT has been available in three licensing ways: commercial, LGPL and GPL, and still complies with QT's dual licensing strategy, table 1-3 shows a brief description of how QT is authorized, and table 1-4 compares how the authorization is used differently.

Table 1-3 how QT is authorized

Qt Business Edition	Qt Commercial licensing applies to the development of proprietary and/or commercial software. This version applies to developers who do not want to share source code with others or follow the GNU Wide general Public License (LGPL) version 2.1 or the GNU GPL version 3.0 terms.
Qt GNU LGPL v. 2.1	This version of QT applies to developing proprietary or Open-source QT applications, provided that the GNU LGPL version 2.1 clause is adhered to.
Qt GNU GPL v. 3.0	If you want to use QT applications in conjunction with software that is limited by the GNU General Public License (GPL) 3.0 version, or if you want the QT application to follow the terms of the GNU License version, this version of QT applies to developing such QT applications.

Table 1-4 qt Authorization matrix

	Commercial edition	LGPL Authorized Edition	GPL Licensed Edition
Licensing Fees	Charge of authorization fee	Free	Free
Must provide source code to change Qt	No, the changed code can not be advertised	Source code must be supplied	Source code must be supplied
Can create proprietary applications	You do not have to advertise the source code	You can, but you must follow the LGPL v. 2.1 section	No, the application is restricted by the GPL and the source code must be exposed.
Provide updates	Yes, only users who are requesting valid maintenance services.	Yes, free release.	Yes, free release.
Support	Provided that the maintenance agreement must be valid.	Not provided, must be purchased separately.	Not provided, must be purchased separately.
Run time charges	Is	Whether	Whether

According to the licensing protocol, QT is released in a different version:

The QT Business Edition is used for commercial software development, offering free upgrades and technical support services.

The QT Open source version is a non-commercial version of Qt and is a unix/x11 version for the development of free and open source software. It can be downloaded and used free of charge under the GNU, GPL or LGPL license.

In addition, QT provides a free evaluation version, snapshots, beta, preview, and many other versions, where the free evaluation of QT for Windows, MAC, Linux, Embedded Linux and Windows CE platform, it not only has full functionality, but also with the source code, Nokia will provide technical support during your assessment. Snapshots, beta releases, and previews are not supported by QT.