PyQt5 is a Python binding of the cross-platform GUI toolkit Qt. Applications built with PyQt5 will run on any platform supported by Qt & Python including Windows, OS X, Linux, iOS and Android.
Created by Riverbank Computing, PyQt is free software (GPL licensed) and has been in development since 1999. PyQt5 was released in 2016 and last updated in October 2021.
For a complete guide to desktop application development with Python & PyQt5, see the PyQt5 tutorial and PyQt5 book Create Simple GUI Applications with Python & Qt.