Earlier quoted context omitted.
It reminds me a lot of Aseprite, which is free to compile yourself since it's open source, but you have to buy it on Steam for auto-updates and such.
Aseprite calls itself "source available" now. Their license has a "no redistribute" clause, so if want to use it and can't compile it yourself, you have to buy it. I spent about an hour trying to compile it on Windows a few months ago, couldn't get it working. Can't remember why, maybe most of that time was installing requirements.
Doesn't really matter because I already had a license, but it would have been interesting to play around with the internals.