AppJar

appJar is a cross-platform Python library for developing GUIs (graphical user interfaces). It can run on Linux, OS X, and Windows. It was conceived, and continues to be developed with educational use as its focus, so is accompanied by comprehensive documentation, as well as easy-to-follow lessons.

License
appJar is licensed under the Apache License v2.0.

History
appJar was originally envisaged as a simple wrapper around tkinter, to allow secondary school pupils to develop simple graphical user interfaces in Python. It was meant to hide away the complexity, so that pupils could focus on writing algorithms, without having to worry about how to position widgets and link to functions. It was started out in the winter of 2014, as a simple in-house project, but soon started to grow. It was published to GitHub on July 31, 2015, and first added to the PyPi repository on 20 December 2016. In June 2017, appJar was featured in an article in The MagPi, detailing how it could be used to interact with Minecraft.

Example
This is a simple "Hello world" example:

The above example is getting even simpler in the 1.0 release (available in beta in the 0.9 release):