A number of years ago I created a couple of projects in B4A... one an interactive fiction creator for a school, the other for our site engineers for Wire and Network schematics... Its Similar to the previous post.
I created these in B4A, I've used a Canvas with Labels and drawn lines and the Pinch and Zoom Lib.
So the user can tap and hold on a node, then move it around keeping the connecting lines connected to the relevant nodes.