Good news for all developers! QT will be available under the LGPL starting with version 4.5. The GNU Lesser General Public License (LGPL) is a free software license published by the Free Software Foundation. The LGPL places copyleft restrictions on the program itself but does not apply these restrictions to other software that merely links with the program. There are, however, certain other restrictions on this software. The LGPL is primarily used for software libraries, although it is also used by some stand-alone applications, most notably Mozilla and OpenOffice.org.
This option could increase Qt usage and adoption. You may see more cross platform commercial application on the Linux desktop. This is huge news for cross-platform developers.
From the announcement page:
The move to LGPL licensing will provide open source and commercial developers with more permissive licensing than GPL and so increase flexibility for developers. In addition, Qt source code repositories will be made publicly available and will encourage contributions from desktop and embedded developer communities. With these changes, developers will be able to actively drive the evolution of the Qt framework.
Qt 4.5 will also be available under commercial licensing terms, while licensing for previous versions of Qt remains unchanged. In addition, service offerings for Qt will be expanded to ensure that all Qt development projects can have access to the same levels of support, independent of the selected license.
Qt, uses C++ with cleaner set of interfaces, widgets, and is "cross-platform" on Windows, Linux, Mac OS X and embedded applications.