Embeddeduse is the blog of a solo consultant who writes about Qt, QML, embedded Linux and Qt licensing.
Commenters praise its article on Qt LGPLv3 licensing as well written and helpful, since they find Qt licensing confusing, and cite it on the LGPL future of Qt.
I have said it once and I will say it again: You really should think twice about buying Qt embedded licenses. Unless you really need an embedded version of Qt the LGPL variant is probably fine for you.
Everyone who is saying that Qt is too expensive -> It's free. Just Use LGPL. All the tools are GPL but that doesn't matter if you don't want to link against those. The Libraries itself are LGPL so you can dynamically link against them with attribution.
Everyone who is saying that they need the Qt Support -> You probably don't. If you live on the bleeding edge you sometimes get cut. Qt for all its flaws really is fine. And if you get stuck the community will help out just as good.
Everyone who is saying that they already bought into it -> Bad news for you. The license terms of the commercial license are very restrictive. If you are building an application which communicates over a network or building a system which consists of multiple programs you have to make sure you don't integrate or communicate with a program which uses the LGPL variant[0]. Yes that's right, if you pay them money you better make sure that you never run your program on KDE because it would inadvertently communicate with software that you are not allowed to communicate with. Of course you are allowed to communicate with everyone while using the LGPL.
ALWAYS use the LGPL variant! Unless you are not able to work within the boundaries of it.
If you have to spend money you are better off donating to the…
Sure, if they don’t mind Qt automatically being relicensing under BSD
“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.“
https://www.embeddeduse.com/2019/12/21/safe-guarding-the-lgpl-future-of-qt/
https://dot.kde.org/2016/01/13/qt-guaranteed-stay-free-and-open-–-legal-update
Here is a good background article: https://www.embeddeduse.com/2019/12/21/safe-guarding-the-lgpl-future-of-qt/
And here the email to which Qt Comany reacts: https://mail.kde.org/pipermail/kde-community/2020q2/006098.html
LGPL has long been a thorn in the side of Qt Company management. Nokia had bought Qt for $150 million, developed and popularized the platform, and then released everything under LGPL. Digia/The Company then bought the intellectual property from Nokia for just 4 million Euros and have been trying to make money from it ever since. Now, with Corona, the management seems to have had a good opportunity to get rid of its annoying obligations to the open source community.
> [0] https://embeddeduse.com/2023/01/06/using-qt-5-15-and-qt-6-under-lgplv3/
That is an excellent link to a well-written article that untangles Qt licensing. Thank you!
I have always found Qt licensing to be almost designed to be as confusing as possible. Unless you deal with Qt on a daily basis it could take weeks to understand what this article lays out clearly in one page. I've always considered the framework to be something "radioactive" to be avoided due to this issue.
The main problem with LGPLv3 is the anti-tivoization clause. That means you should basically provide the end user a way to replace the Qt libraries with their own. On embedded systems this can mean headaches for companies releasing commercial products.
More details:
https://embeddeduse.com/2016/04/10/using-qt-5-6-and-later-under-lgpl/
Qt from 4.8(?) To 5.6 offered an LGPL2 license too but after that it's mostly LGPLv3 i think.
> An application using Qt Commercial must not communicate with any another application using Qt LGPL-3.0 or Qt GPL, if both applications run on the same device. This is more restrictive than GPL.
https://embeddeduse.com/2023/01/06/using-qt-5-15-and-qt-6-under-lgplv3/