Markdown by DaringFireball - Text-to-HTML conversion tool/syntax for web writers, by John Gruber
GitHub Flavored Markdown - GitHub uses "GitHub Flavored Markdown," or GFM, across the site--in issues, comments, and...
DocBook - DocBook is a schema (available in several languages including RELAX NG, SGML and XML DTDs, and W3C...
Texy! - Texy! is a lightweight markup language as well as converter of this format to XHTML, in a form of a...
pandoc - Pandoc is a Haskell library for converting from one markup format to another, and a command-line...
StackEdit - Full-featured, open-source Markdown editor based on PageDown, the Markdown library used by Stack Overflow and the other Stack Exchange sites.