by Evan Solomon on WordPress.org
WordPress plugin to let commenters use (GitHub-flavored) Markdown, and turn it into HTML.

Example of pre- and post- converted text (live previews are not (yet) includeded in the plugin).
Comment forms allow some HTML, this plugin extends that to let users type in Markdown and have it automatically converted to HTML. It also extends Markdown with a couple features made popular by GitHub. Conversion from Markdown to HTML is completely automated and doesn’t require anything on the commenter’s part.
The feature additions from GitHub are:
Two notable features from GitHub’s Markdown implementation are missing:
GitHub-Flavored Markdown Comments is developed, unsurprisingly, on GitHub.