GTK

Free and open-source cross-platform widget toolkit

GTK (GIMP Toolkit) is a free and open-source cross-platform widget toolkit for creating graphical user interfaces. Originally developed for the GNU Image Manipulation Program, it became the foundation of the GNOME desktop environment. GTK is written in C but offers bindings for many languages including Python, Rust, and JavaScript. It provides a comprehensive set of widgets, a CSS-based theming system, and supports Wayland and X11 display backends on Linux as well as Windows and macOS.