Yes, I have. Here's some to name a few: GTK, Qt, wx, Fox, fltk...
Yes, I agree, Qt just works. My initial point was and still is about interoperability. They don't all speak well with each other and there are many good, useful applications in toolkits other than Qt or GTK.
What do you even mean by "they don't all speak with each other", what are they, and what can't they do (that electron can do?).
With Qt I can use the clipboard, sockets, and so on, set an icon for the application. Linux applications have standards to follow, as long as they do they look the same to the desktop environment.
Are electron apps magically able to speak with other electron apps, in a simpler way (to implement) than Qt applications? I don't think so.
Yes, I agree, Qt just works. My initial point was and still is about interoperability. They don't all speak well with each other and there are many good, useful applications in toolkits other than Qt or GTK.