Notching pipes correctly is hard. A common technique is to model a pipe, export the outer surface of the pipe and "unroll" that cylindrical surface so it becomes flat. Then this flat pattern gets printed and cuttout. This cuttout is then wrapped around a pipe and taped to it. Now you've got a clear contour to follow with your cutting tools.
The problem in these steps is the amount of steps it takes to unfold a 3d model into a flat pattern and have it ready for printing. This program enables the user to input an STL 3d model of the notched pipe. The program output is a 2D outline of the cuttout that can be printed. No need to deal with unfolding or worrying about surfaces.