http://doc.trolltech.com/3.3/faq.html#1-1
What is Qt?

Qt is a multiplatform C++ GUI toolkit. It provides application developers with all the functionality needed to build applications with state-of-the-art graphical user interfaces. Qt is fully object-oriented, easily extensible, and allows true component programming.

Qt is supported on the following platforms:

* MS/Windows -- 95, 98, NT 4.0, ME, 2000, and XP
* Unix/X11 -- Linux, Sun Solaris, HP-UX, Compaq Tru64 UNIX, IBM AIX, SGI IRIX and a wide range of others
* Macintosh -- Mac OS X
* Embedded -- Linux platforms with framebuffer support.

It has become the emerging standard development environment for IT professionals who want to:

* Write (and maintain) a single source-tree.
* Port their applications to multiple platforms with a simple recompilation.
* Internationalize their applications.
* Provide their applications with native look and feel.
* Have their applications run at native speed.