It is a handwritten memo app.
It is a simple app with reduced functionality.
There are only four buttons below.

"UNDO" will return to the previous operation.
"REDO" restores the process that was canceled immediately before.
"BACK" will return to the previous screen.
"RESET" clears the screen.

If you want to save the screen, please use the screen shot of the standard function of your smartphone.