Slint is under multiple license, including the open-source GPL and a royalty free license. What specifically bothers you about the licensing? (I work on Slint, genuinely curious)

Probably that it's not non copy left like MIT so they can't just use it without sharing code back.

For free without paying, like the other GUI frameworks.

Correct. This is a class of products that I really would rather not go commercial for. It's extremely difficult to change after the fact so from a business standpoint it puts us in a place where if the vendor decides to start cranking prices or they sell their business and the new owner does, then we are in a really difficult position.

It's not actually about paying money or not, I've signed up for many a patreon or what not to support open source projects I use. I fully believe in paying people for software. But for core things like this I do prefer MIT/APACHE.

But Slint is open source and you can for it if we were to change the license, and the royalty free license is free of charge.

Even MIT/Apache software can change license and start charging, as we've seen in the past with some project.

My app is proprietary though, so I can't use the royalty free license. I've definitely licensed commercial software before. For example, I've licensed OCR software for many years.

The difference to me is that with OCR I can change it out with acceptable effort in the case that the vendor does something that we can't agree to. But it's just too hard to swap out a UI library. That's a major rewrite. It's too risky, to the point I'd rather spend resources bringing an MIT/APACHE UI kit up to my needs than risk being locked in with a vendor.

The royalty free license is free of charge, no need to pay