wxWidgets - wxWidgets: Cross-Platform GUI Library
PyQt - Riverbank | Software | PyQt | What is PyQt?
GTK - GTK+ is a multi-platform toolkit for creating graphical user interfaces.
Tkinter - Tkinter is a Python wrapper for Tcl/Tk that offers classes to create various graphical user interfaces.
Electron - Build cross platform desktop apps with web technologies
MD Python Designer - A drag and drop GUI Designer that uses a combination of Tkinter and its own code.