Mark Jaquith

This plugin allows you to compose content in Markdown on a per-item basis. The markdown version is stored separately (in the <code>post_content_filtered</code> column), so you can deactivate this plugin and your posts won’t spew out Markdown, because HTML is stored in the <code>post_content</code>, just like normal. This is also much faster than doing on-the-fly Markdown conversion on every page load. It’s only done once! When you re-edit the post, the markdown version is swapped into the editor for you to edit. If something external updates the post content, you’ll lose the Markdown version.
Note: this plugin assumes you’re using the Classic editor.

Markdown on Save

Allows you to compose content in Markdown on a per-item basis. The markdown version is stored separately, so you can deactivate this plugin any time.

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.

Markdown on Save vs Markdown Editor