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My interpretation is you can build commercial products with Qt for free as long as you can comply with LGPL. Mostly this means link dynamically (if closed source), only use LGPL components and give attribution.

Lots of GUI native, non-web libraries have been started in Rust, but they are VERY far from being close to what Qt supports. You may get closer using web based libraries (Tauri, etc), but I wouldn’t personally start web based desktop applications.

Exactly! There's always misunderstanding about Qt's license that I believe they should make the LGPL license clearer on their website. I believe many developers are struck down because they think it's not permissive enough where actually it's quite permissive.

One problem with Qt is that some modules are under the GPL and it is easy to end up inadvertently with a GPL dependency. Also it seems the Qt company makes it confusing on purpose.

> Also it seems the Qt company makes it confusing on purpose.

Yes, things have changed. So annoying you can't just download an offline installer using a mirror of your choice, for example.

> One problem with Qt is that some modules are under the GPL and it is easy to end up inadvertently with a GPL dependency.

I never encountered such a problem, the GPL modules always seemed very niche and targeted toward specific industries (automobile, etc).

Some of it might be misunderstanding, but complication of distribution may also play a role. Making sure that your application is correctly dynamically linked and packaged to run without issues across all supported platforms and configurations can be considerably more involved than statically linking depending on the toolchain in question.

Which on that note, last I knew getting Qt apps correctly stripped and packaged for all platforms was a bit of a bear. In particular I remember building Mac application bundles being messy.

This is true, but then again, these days, it's easy to look up at a popular open source Qt app and copy its CI recipes. For example, anyone that wants recipes for creating binaries for multiple operating systems can copy the GitHub workflows in my open source note-taking app: https://github.com/nuttyartist/notes/tree/master/.github/wor...

That said, I really think Qt should have a separate commercial license that is exactly like LGPL but allows you to link statically and costs much less (without all the enterprisy things).

The only issue though is that Qt does not agree that mobile apps on app stores can use LGPL license due to anti-tivotization clause. Nevertheless they do have a somewhat reasonable pricing for small business of 500$ per year.

What cocoa19 says. Also there is a small business license that is quite affordable to commercial indie developers and gives access to all modules.

I think Slint is quite interesting, but it's licensing model is very similar to Qt, albeit somewhat more restrictive: The open source option is GPL v3 (not LGPL), and then there's commercial licenses, which yes, are cheaper - for now, for a start-up toolkit.

Pricing can change. Yes, there's a perpetual "Buyout" license for $5k, but they can probably just rename the product and claim it's a new one (or add a second product and add commercially relevant eggs to that basket; Qt has tried with things like "Qt for Device Creation" and "Qt for Automotive").

The open source option is not backed by a poison-pill protection like the Free Qt Foundation agreement either.

I know the people behind Slint, and I have a lot of trust toward them. But ownership can change, too.

Slint is under three licenses: There The GPL for open source users, the royalty-free license for proprietary desktop application (which is free of charge), and the commercial license.

The royalty free is even better than the LGPL for Rust because rust doesn't support dynamic linking or even re-linking with object files.

Based on the discussion with our community, we added a clause in our CLA - https://cla-assistant.io/slint-ui/slint - to ensure that Slint will always be made available under an open source license as well as a royalty-free license.

"We believe that open-source software development and communities are the foundation for a healthy ecosystem of high-quality software, where everyone can learn, improve and give back. We commit to upholding this foundation and pledge by promising to continue to develop Slint in the open under an open-source license compliant with the Open Source Definition.

Further, we commit to provide a royalty-free license for those who develop desktop or web applications and do not want to use open-source components under copyleft licenses."

> some of the QT libraries or older forked versions of them are still completely under open source license

Qt is LGPLv3 + GPLv3 which are clearly open source licenses.

The Qt Company sheds a lot of FUD on their licensing as an attempt to strongarm customers into paying for Qt. For a lot of companies, Qt's LGPL version would work just fine, but Qt will breathe down your neck trying to get you to switch.

Source: I work in a company that heavily uses Qt

> if you have commercial aspirations with your project

1. Nothing in copyleft licenses forbids you from making a living or receiving money.

2. Since the post was about writing an effect for KWin and your alternatives do nothing of sort… perhaps they aren't really valid alternatives, at least in this context.