[Maruku]: http://maruku.rubyforge.org
[PHP Markdown Extra]: http://michelf.com/projects/php-markdown/extra/
[Pandoc]: http://johnmacfarlane.net/pandoc/
[MathJax]: http://www.mathjax.org
[BlueCloth]: http://deveiate.org/projects/BlueCloth
[RedCloth]: http://redcloth.org/