Evan Solomon

Comment forms allow some HTML, this plugin extends that to let users type in <a href="http://daringfireball.net/projects/markdown/" rel="nofollow ugc">Markdown</a> and have it automatically converted to HTML. It also extends Markdown with a couple features made popular <a href="https://github.com/github/github-flavored-markdown" rel="nofollow ugc">by GitHub</a>. Conversion from Markdown to HTML is completely automated and doesn’t require anything on the commenter’s part.
The feature additions from GitHub are:
<ul>
<li>Single linebreaks are treated as new paragraphs</li>
<li>Code “fencing” with three backticks (“`)</li>
</ul>
Two notable features from GitHub’s Markdown implementation are missing:
<ul>
<li>To do lists: Doing these well would require some front end interaction, which I decided is outside the scope of this plugin at least for now</li>
<li>Repository autolinking (e.g. comments, issues, etc): These seemed a little too GitHub-specific.</li>
</ul>
GitHub-Flavored Markdown Comments is developed, unsurprisingly, <a href="https://github.com/evansolomon/wp-github-flavored-markdown-comments" rel="nofollow ugc">on GitHub</a>.

GitHub-Flavored Markdown Comments

WordPress plugin to let commenters use (GitHub-flavored) Markdown, and turn it into HTML.

seothemes

Markdown Editor replaces the default WordPress editor with a Markdown editor for your posts and pages. This plugin uses the Jetpack Markdown module for converting Markdown into HTML and plays nicely with Jetpack if both plugins are installed.
There are 4 editor layouts to choose from when writing posts: default, preview, full-screen and split screen. Changes are updated automatically allowing you to preview your content as you write.
By default Markdown Editor is only enabled on Posts, but you can enable it on pages and custom post types by adding post type support. For example to add Markdown support to Pages, add the following line of code to your theme’s functions.php file:
<pre><code>add_post_type_support( 'page', 'wpcom-markdown' );
</code></pre>
To add Markdown support to a ‘Product’ custom post type, add this to your theme’s functions.php file:
<pre><code>add_post_type_support( 'product', 'wpcom-markdown' );
</code></pre>
<h3>Syntax Highlighting</h3>
By default, Markdown Editor enables syntax highlighting for code blocks. This can be removed by adding the following line of code to your theme’s functions.php file:
<pre><code>add_filter( 'markdown_editor_highlight', '__return_false' );
</code></pre>
The click to copy button can be removed with the following line:
<pre><code>add_filter( 'markdown_editor_clipboard', '__return_false' );
</code></pre>

Markdown Editor

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Kills WordPress

Replaces the default WordPress editor with a Markdown editor for your posts and pages.

GitHub-Flavored Markdown Comments vs Markdown Editor