I wrote some simple ascii diagrams inline with readme and code, but never too serious. I wrote this tool to enhance the rendering of the diagram, and publish it opensource. I never did expect some people use it seriously https://github.com/ivanceras/svgbobrus/pull/6

I've used this for quick-and-dirty ASCII diagrams. They might need a bit of touching up to be usable with Spongedown. http://asciiflow.com/