Trolltech has released Qt/Mac under the GNU General Public License (GPL), meaning Mac developers can use the code in software development at no charge.

Qt/Mac is the Mac port of Qt, a single-source, multiplatform C++ GUI tool kit that allows applications to run natively on Windows, Linux and Unix, and OS X from the same codebase.

A requirement of this licence is that any software produced with this version of Qt/Mac must be released with its full source-code available under the GPL. Developers wanting to create commercial software can continue to do so using the existing Qt/Mac commercial licenses.

The move opens the floodgates for developers wishing to bring software developed with Qt/X11 to OS X. Most of these applications require a simple recompile, the company said.

Trolltech president and co-founder Eirik Eng said: "This dual-licensing strategy has been key to Trolltech's success."

The software is available for download.