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The Q Public License (QPL) is a non-copyleft license, created by Trolltech for its free edition of the Qt. It was used until Qt 3.0, as Trolltech toolkit version 4.0 was released under GPL version 2.
It fails the Debian Free Software Guidelines, used by several Linux distributions, though it qualifies for the Free Software Foundation's Free Software Definition; however, it is not compatible with the FSF's GNU General Public License, meaning that products derived from code under both the GPL and the QPL cannot be redistributed.
KDE, a desktop environment for Linux, is based on Qt. Only the personal edition of Qt was covered by the QPL; the commercial edition, which is functionally equal, is under a pay-per-use license and could not be freely distributed. Meanwhile, the Free Software Foundation and authors of the GPL objected to the QPL as it was a non-copyleft license incompatible with the GPL. As KDE grew in popularity, the free software community urged Trolltech to put Qt under a license (the QPL) that would assure that it would remain free software forever and could be used and developed by commercial third-parties. Eventually, under pressure, Trolltech dual-licensed Qt for use under the terms of the GPL or the QPL.
Other projects that have adopted the Q Public License, sometimes with a change in the choice of jurisdiction clause, include:
- The OCaml compiler and related tools from Projet Cristal at INRIA
- LibreSource is a versatile collaborative platform provided by artenum and dedicated to collaborative software development
- Jpgraph is a graph generation tool written in PHP that dynamically produces charts and graphs as image files for presentation on websites.
- Hercules, a software implementation of the System/370, ESA/390, and z/Architecture mainframe computer architectures.
- CGAL for versions 3.x. The CGAL library is released under GNU General Public License since CGAL version 4.0 (March 2012).
- Tgif (program) switched from a free-of-charge non-commercial license to the Q Public License.
The Debian project rejects software covered by solely QPL (and not dual licensed with something else like the GPL) because of:
- A choice of venue clause
- Forced distribution to a third party
- Forced blanket license to the original developer
All legal disputes about the license are settled in Oslo, Norway, but it has never been legally contested.
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