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.

Dev7studios

Typewriter completely removes the “Visual Editor” feature in WordPress and replaces it 
with a simple Markdown editor so that you can join sites like StackOverflow and Github in writing in the 
simple and growingly popular <a href="http://daringfireball.net/projects/markdown" rel="nofollow ugc">Markdown format</a>.
For the more technical among you, Typewriter removes the TinyMCE editor and defaults to a Markdown specific “Text” editor 
and parses the output using MarkdownExtra.

Typewriter

Typewriter replaces the Visual Editor with a simple Markdown editor for your posts and pages.

Markdown Editor vs Typewriter