Qt is a cross-platform application development framework, widely used for the development of GUI programs, and, since the release of Qt 4, also used for developing non-GUI programs such as console tools and servers. Qt is most notably used in KDE, the web browser Opera (Linux/FreeBSD/Solaris versions), Google Earth, Skype, Qtopia and OPIE. It is produced by the Norwegian company Trolltech, formerly Quasar Technologies. Trolltech insiders pronounce Qt as “cute”.

For moar info, see: Qt (toolkit)

• Qt Homepage
• Trolltech Labs and Developer Blogs
• The GPL Versus Qt "War" (19.2.3) (regarding Qt licensing from before version 2.2)
• How Qt's proprietary license agreement works
• An Introduction to Design Patterns in C with Qt4. Excerpts from a Prentice Hall book teaching C programming from the ground up, using Qt 4.1