I've been fascinated with the M5Paper ever since I received it and wanted to use it to build some home automation controller that runs for a long time on the battery.
Now, when I started looking into the UI code of the Factory Test application, I thought I could easily extend it but unfortunately, the code is not really well documented and a weird mix of C and C++. This is where I started with my project to build a library for UI development on the M5 paper that is generic enough to be easily extended and make it easy to build nice looking and usable applications. For example the Tic Tac Toe application is about 300 lines of easy to reason about code.
Right now it's in the beginning, but feel free to check out the source code here https://github.com/grundprinzip/M5PaperUI I'm planning to extend it with simple text fields, settings application for wifi configuration etc.
Below are some example images from the project: