So, what exactly is this draw.io diagramming web app that is
becoming popular? Is it open-source or proprietary? Indeed, it is
open-source. With some clicking around and looking, you can find its
source code here.
20190102/https://about.draw.io/
20190102/https://about.draw.io/about-us/
20190102/https://github.com/jgraph
20190102/https://github.com/jgraph/drawio
20190102/https://github.com/jgraph/mxgraph