I nominate the Rust/FLTK GUI bindings.
I use this library to build distributable single file GUI executables. I build binaries for both Windows and Linux. (FLTK also runs on Mac but I've not tried it.)
What I especially like is that they "just work"; the dependencies on Windows and Linux are light, the size added to executables for the GUI lib is light (<1MB), and FLTK is versatile: you can quite easily customize a plain widget to draw what you want and behave (i.e., catching mouse clicks and key presses) how you want.