Secrets of Mental Math details some excellent techniques for doing complex arithmetic in your head. These techniques work great, but I needed practice and for once I found that there isn’t an app for that…until now!
Kivy is a Python user interface library for development of touch-based, modern UI applications.
One useful feature of Kivy is that you can copy the Python code to your Android phone’s SD card and launch the app with the Kivy Launcher.
All code is available in the MentalMath GitHub repository.