et http://www.bortzmeyer.org/7764.html Guidance on Markdown: Design Philosophies, Stability Strategies, and Select Registrations

Markdown site http://daringfireball.net/projects/markdown/ and play online http://daringfireball.net/projects/markdown/dingus

Babelmark to try and compare markdown implementations
ex: http://johnmacfarlane.net/babelmark2/?text=Here%27s+a+list+of+stuff%3A%0A*+item+one%0A*+item+two%0A*+item+three%0A

CommonMark https://commonmark.org/ et specs: https://spec.commonmark.org/