This app (Awesome CNN) is a work in progress. It's large and unwieldy and doesn't work predictably all the time, but it is an example of a 'Convolutional Neural Network'.
The app was written in Python. It is tuned to recognize either numbers or letters, but not both at the same time. In truth it is terrible at recognizing letters and only slightly better at numbers.
The source code for the neural network used is available on Github at the following url:
This is the url for the original project which is tuned for only digits. That task is more reasonable than the one that I tried, which is to tune the NN to various alphabetic letters.
Hopefully in the near future I will publish the source code for the android app, and then I will update this blog.