PyGTK
PyGTK lets you to easily create programs with a graphical user interface using the Python…
15 Alternatives To PyGTK
Agar
Agar GUI
Avalonia
A multi-platform .NET UI framework
BeeWare
Write your apps in Python and release them on iOS, Android, Windows, MacOS, Linux, Web, and tvOS…

Crazy Eddies GUI System
Crazy Eddie’s GUI (CEGUI) system is a graphical user interface C++ library.
FLTK
Fast Light Toolkit - Fast Light Toolkit (FLTK)

Fox toolkit
fox-toolkit.org
JUCE
JUCE is a wide-ranging C++ class library for building rich cross-platform applications and plugins…
LambdaNative
LambdaNative is a cross-platform development environment written in Scheme, supporting Android…
Nana C Library
Nana C++ Library - a modern C++ GUI library
PySide
Qt for Python - Qt Wiki
Qt
C++

Qt Creator
Qt Creator is a cross-platform C++, JavaScript and QML integrated development environment. It is the fastest, easiest and most fun experience a C++ developer could wish for.
Uno Platform
Build Mobile, Desktop and WebAssembly apps with C# and XAML.

wxSVG
wxSVG is C++ library to create, manipulate and render SVG files.
wxWidgets
wxWidgets: Cross-Platform GUI Library