The history is a bit convoluted. Let me see if I can help untangle it:

- In 2006, Niklas Frykholm created `markdown.lua` [1], a regex-based
  Markdown parser written in Lua.

- In 2009, John MacFarlane, the founder of Pandoc, created Lunamark [2],
  an LPEG-based Markdown parser that was ca three orders of magnitude
  faster than `markdown.lua`. Around 2011, there is a bunch of commits
  with speed optimizations by Hans.

- In 2016, I created the Markdown Package for TeX [3] as a fork of
  Lunamark [3]. Initially, I would contribute fixes upstream and take
  them downstream. In 2023, there was a significant rewrite to support
  the CommonMark standard [4], which makes our code base largely
  incompatible with Lunamark. We are actively developed with monthly
  releases.

  Confusingly, the Markdown Package for TeX contains a file titled
  `markdown.lua` even though there is no relation to Niklas Frykholm's
  code.

 [1]: http://www.frykholm.se/files/markdown.lua
 [2]: https://github.com/jgm/lunamark
 [3]: https://github.com/witiko/markdown
 [4]: https://spec.commonmark.org/

I hope this clears things up.