The little known KDE Free Qt Foundation makes sure that Qt stays free and open-source. It guarantees that all Qt modules currently licensed under LGPLv3 must continue to be available under LGPLv3 in the future. This covers all modules from Qt Essentials and many add-on modules. If The Qt Company discontinued the FOSS version of Qt, the Foundation would have the right to make Qt available under the BSD license. This is a very powerful protection of free and open-source Qt.

Although I have been working with Qt for 20 years and for the Qt business unit of Nokia from 2009 to 2012, I haven’t been aware of the KDE Free Qt Foundation and its importance. This changed when I stumbled over the blog post A better Qt because Open Source and KDE by Olaf Schmidt-Wischhöfer. Olaf writes that the background for his post (emphasis mine)

[…] is the wish of The Qt Company to change some of the contract provisions. It is still a bit unclear which ideas exactly they are pursuing, but we will need to have a public consultation on them in any case.

Olaf is one of the board members of the Foundation. The Foundation has four board members, two from KDE and two from The Qt Company. If there is a tie in a vote, the KDE members decide. In other words, the KDE board members have veto power.

You find the Software License Agreement (SLA) between The KDE Free Qt Foundation and The Qt Company here. The SLA has been modified with every major release (Qt 2.x, Qt 3.x, Qt 4.x and Qt 5.x). So, it’s not surprising that The Qt Company wants some changes now that Qt 6 is less than a year away.

This SLA governs the licensing for the modules in the Qt Free Edition. The Qt Free Edition consists of all the modules from Qt Essentials (e.g., Core, Multimedia Network, QML Quick), many modules from Qt Add-Ons (e.g., 3D, Bluetooth, NFC, OpenGL, Serial Port, WebEngine) and many Qt Tools (e.g., Creator, Designer, Linguist, qmake) (see Section 1.8 in the SLA and the documentation page All Modules).

The SLA requires The Qt Company to release at least one minor or major Qt version every 12 calendar months (see Section 3). It forbids The Qt Company to keep changes or extensions of the Qt Free Edition closed for more than 12 months. Contributions to Qt must also be published within 12 months. If The Qt Company fails to comply with any of these conditions, the Foundation has the right to release the Qt Free Edition under the BSD license.

The BSD license would allow any company, group or person to do with Qt whatever they want. They could even sell Qt under their own terms. The BSD threat is a strong guarantee that Qt will stay free and open-source and that it will get regular significant updates.

The Qt Free Edition must always be published under GPLv3 or a license compatible with GPLv3 (see Section 4.3). The Foundation considers GPLv3 and not LGPLv3 as the standard license for the Qt Free Edition. However, Qt Essentials must always be available under LGPLv3 (see Section 4.4). Qt Tools and Applications must be released under GPLv3 with Exceptions (see Section 4.7).

New Qt Add-Ons need only be available under GPLv3 (section 4.5). If, however, a Qt Add-On or any other part of the Qt Free Edition existed under a license different from GPLv3 at the signing date of the SLA, it must be kept under this other license as well. So, all parts of the Qt Free Edition now available under LGPLv3 will be available under LGPLv3 in the future (see Section 4.6).

The licensing of the Qt Free Edition can only be changed if three of the four board members agree. As two board members are from the Foundation and the Foundation decides on a tie, The Qt Company has no way to change the licensing on its own.

The non-profit KDE Free Qt Foundation ensures that Qt Essentials and many Qt Add-Ons remain available under LGPLv3 and that most Qt Tools under GPLv3. They also ensure that the Qt Free Edition gets new features every year.

Many of us save money from using the Qt Free Edition. Let us donate some of this money to the Foundation (a part of KDE e.V.) so that we can enjoy our freedom for many years to come. Thanks to the Foundation for their important work!