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.

crimson090

Adds buttons to the Text (HTML) edit which generate Markdown syntax. These buttons serve as a great introduction to 
users who are new to Markdown, as well as shortcuts for more experienced users. The buttons include:
<ul>
<li>Bold</li>
<li>Italic</li>
<li>Blockquote</li>
<li>Link</li>
<li>Code</li>
<li>Table</li>
<li>Headers</li>
<li>Help (links to external Github Markdown guide)</li>
</ul>
This plugin does not modify the Visual editor, as that editor is not ideal for writing Markdown in. It’s recommended you disable 
the Visual editor entirely to enforce using Markdown.
Note that this plugin does not render Markdown. You should use a plugin (such as Jetpack Markdown) to render markdown in your theme.

MarkdownBar

Adds a toolbar of buttons to the Text (HTML) edit which generate Markdown syntax

Markdown on Save vs MarkdownBar