https://www.aseprite.org/, looks like a really nice pixel art editor / sprite editor.
The author needs to eat, therefore relicense (I think).
It seems like this is the crux of the matter: https://dev.aseprite.org/2016/09/01/new-source-code-license/ and https://github.com/aseprite/aseprite/issues/1666 https://github.com/aseprite/aseprite#license
In my opinion it's the author who should have been seeking a fork then. Getting the approval of all the contributors to do so, knowing that those people won't be able to help anymore.
Also, that kind of thing is usually handled by a Pro version or advanced support for paid subscribers.
A project being GPL'd doesn't necessarily mean the copyright isn't owned by one party.
He's clearly the top contributor, but not the sole contributor.
Sadly, it's why there's more and more projects adopting CLAs. Some that say that all the code you're contributing is owned by the project and not yourself. Allows for future relicensing in some cases.
In that case it looks like most of the other contributors contributed after the CLA was added but there are still a few commits from before that point. Accordingly he should have sought permission from those people before changing the license.
I contributed a few minor fixes and got an email from David asking for permission to re-license.
You're conflating CLA and CTA/CAA, the difference is explained here [1], and it matters.
[1] https://opensource.stackexchange.com/questions/860/what-is-t...
People should read at least title of this news: "LibreSprite – fork of last open-source release of Aseprite pixel art editor".
If they will open link then they could read "History" chapter in README.md[0]
[0] https://github.com/LibreSprite/LibreSprite/blob/master/READM...