Mermaid is a JavaScript-based diagramming and charting tool that uses Markdown-inspired text definitions and a renderer to create and modify complex diagrams. The main purpose of Mermaid is to help documentation catch up with development.

https://github.com/mermaid-js/mermaid 

 @1efe3b1d also check out plantuml https://github.com/plantuml/plantuml 

 @1efe3b1d A bit like https://pikchr.org/ that the fossil/sqlite creators made