[ColonelPhantom]

I think wxWidgets was pretty big in the 2000's, with quite some programs using it. To name one example, the Code::Blocks IDE uses it.

FLTK has never seen adoption even to the level of wxWidgets I think, but to be honest it is also quite simply hideous. I have not found a proper looking theme for it either, since I was mildly interested in using it to add a simple GUI to a Rust tool.

[luvs2code]

I don't know why WxWidgets seems to be less popular now than it was back then. I remember it being somewhat popular. Now people hardly seem to know about it.

FLTK looks horrible next to most modern applications. But FLTK 2.0, which has been abandoned for 10 years, actually looks pretty modern and the API is actually pretty elegant. There was some kind of split in the community about FLTK 2.0 breaking backward compatibility and I guess the 1.0 people won in the end.