I started to learn how to use FLTK in Rust this year, so its fair to assume this update is specifically made for me; its so obvious. FLTK is basically a suckless toolkit for GUIs, with the goal of being small, light and standalone without being complicated. It is very small and can be compiled into the app without runtime requirements. It has most common functionality you would expect from a toolkit and should work cross platform.
Happy to see this update! Need to experiment and learn more about it soon for my first FLTK app.
FLTK compared to GTK and QT is lightweight, less complicated to learn and program in and is statically linked, meaning no runtime dependency required, while still being very small in binary size. As an example the FLUID program to create a GUI itself contains every widget and the binary is only half a megabyte. More about FLTK here: https://www.fltk.org/doc-1.3/intro.html