The tkinter package (“Tk interface”) is the standard Python interface to the Tcl/Tk GUI toolkit. Both Tk and tkinter are available on most Unix platforms, including macOS, as well as on Windows systems.
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The Fast, Light Toolkit (FLTK, pronounced fulltick) is a cross-platform graphical user interface (GUI) library developed by Bill Spitzak and others. Made to accommodate 3D graphics programming, it has an interface to OpenGL, but it is also suitable for general GUI programming.
Gio is a library for writing cross-platform immediate mode GUI-s in Go. Gio supports all the major platforms: Linux, macOS, Windows, Android, iOS, FreeBSD, OpenBSD and WebAssembly.
Repose is a Rust UI framework with a Compose-like programming model. It's organized as a small core (repose-core) plus higher-level UI/layout (repose-ui) and platform runners (repose-platform) that currently target desktop (winit) and Android, with web support.
