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.

Benjamin Chris

WP Editor.md is a beautiful and practical Markdown document editor.
Build support for the WordPress using Editor.md.
The plugin uses the Markdown module from WordPress <a href="http://jetpack.me" rel="nofollow ugc">Jetpack</a> for parsing and saving content.Thank for Jetpack modules.

Markdown on Save vs WP Editor.md – The Perfect WordPress Markdown Editor