I dunno, that isn't terrible.

The terrible part is where if you pay for a commercial license to use it in a proprietary application, you can't stand within 50 feet of the LGPL version.

https://www.qt.io/terms-conditions/:

“Prohibited Combination” shall mean any effort to use, combine, incorporate, link or integrate Licensed Software with any software created with or incorporating Open Source Qt, or use Licensed Software for creation of any such software.

So you can't use KDE to write a program that links against the proprietary QT libraries.

> So you can't use KDE to write a program that links against the proprietary QT libraries.

The way I read it that's fine, it's the other way around that's forbidden - you're not allowed to use the commercial-licensed version to work on KDE.

I think what it's saying is that you can't use licensed Qt to create software that uses both it and OSS Qt, not that you can't use software that uses OSS Qt to create software that uses licensed Qt.

Is it ABI compatible? You could run KDE with the proprietary libraries.

That would be violating the proprietary licence terms

Forgive me if I'm missing something obvious, but could you explain why that is?

KDE was created with open source Qt. As in, the developers that wrote KDE used the LGPL version of Qt.

To repeat myself, “Prohibited Combination” shall mean any effort to use, combine, incorporate, link or integrate Licensed Software with any software created with or incorporating Open Source Qt.

Oh goodness, I'm so sorry you had to repeat yourself.. The reason I started my question by saying "forgive me if I'm missing something obvious" is because I'm no expert on licensing issues and was asking a genuine question.

if Qt is a true open source project, it will be way more widely used these days, its commercial model hurts itself badly.

make it fully truly open source, charge premium for those who need your professional service to make profits, then it will fly to the sky.

I think you have a different definition of "open source" than I do at least. LGPL is (IMHO) a true open source license.

I agree though that some licensing changes would really help them grow. I think they've hurt long term adoption in exchange for short term revenue. I don't blame them, baby needs new shoes after all, but as a huge fan of Qt I would love to see them become a standard. The product is good enough that they deserve it, but the license can be a bit scary for people who aren't already familiar with it.

Qt's site does seem to be trying to scare you into believing that you can't possibly comply with the LGPL and you really really should buy the commercial license, for your own sake.

LGPL isn't really that onerous though..

However, new modules in Qt 6 and any rewrites of modules Qt 5-> 6are now GPL, which is rather copy-left and will spread to the rest of your code.

>However, new modules in Qt 6 and any rewrites of modules Qt 5-> 6are now GPL

That's very surprising, it would make upgrading from Qt 5 to Qt 6 a no-no for the small companies who use Qt LGPL. I'm sure they want to keep developer mindshare. Which LGPL Qt 5 modules became GPL in Qt 6?

caveat is that, quite a few pieces here and there are not LGPL, and it's not so easy for beginners to figure out how to do it the right way, I was one of them.

> charge premium for those who need your professional service to make profits

How exactly does that work? Why would the company invest a lot in the library if they can just offer professional services without it? For example, KDAB already offer professional services around Qt and do not need to spend much in R&D.

I believe GP is sarcasm for recent Red Hat situation

It's one of the most common UI libraries I've seen. It seems to work out well from them.

The "success" of others prove otherwise.