The gtk-fortran binding (https://github.com/vmagnin/gtk-fortran/wiki), developed since 2011, is based on the ISO_C_BINDING module, introduced in the Fortran 2003 standard, which is used to interface fortran programs with the functions of the GTK libraries (mainly written in C). gtk-fortran is multi-platform: Linux, FreeBSD, MacOS, Windows (via MSYS2), and even Raspberry Pi (ARM processor)...
GTK being a collection of libraries (GTK, Pango, GDK, ATK, Cairo, GdkPixbuf, GLib...), a python script parses the hundreds of GTK header files and generates around 10000 Fortran / C interfaces. A supplementary High Level library can ease programming, and PLplot can also be used in gtk-fortran. The user can learn to create Graphical User Interfaces using its wiki documentation and the commented Fortran examples.
We will finally speak of the new GTK 4 development branch, our objective being to be ready for the release of that next major version around the end of the year. We will also present some ideas for the future and a SWOT analysis of the project.