CommonMark

CommonMark aims to be a standard, unambiguous syntax specification for Markdown, along with a suite of comprehensive tests to validate Markdown implementations against this specification.

It was created in 2014 when the authors of various Markdown parsers/implementations got together to formalize the Markdown specification.

The name CommonMark was chosen after the original Markdown author, John Gruber, objected to the use of the name Markdown.