user manual: https://pikchr.org/home/doc/trunk/doc/userman.md
online playground: https://pikchr.org/home/pikchrshow
Kernighan's paper on PIC that inspired it
there is a go port as well
Pikchr (pronounced "picture") is a PIC-like markup language for diagrams in technical documentation. Pikchr is designed to be embedded in fenced code blocks of Markdown or similar mechanisms of other documentation markup languages.
compare to mermaid.js, plantUML, d2