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.

Terry L.

Generation of diagrams and flowcharts from text in a similar manner as markdown by using <a href="https://mermaid.js.org/" rel="nofollow ugc">mermaid.js</a>
WP Mermaid is smart enough that loads mermaid.js only when your posts contain Mermaid syntax, by detecting the use of shortcode and block. So it will not be loaded on your website everywhere.
= See also
If you are looking for a <a href="https://github.com/terrylinooo/githuber-md" rel="nofollow ugc">Markdown editor</a> supporting Mermaid, you can also check out my WordPress plugin called the <a href="https://wordpress.org/plugins/wp-githuber-md/" rel="ugc">WP Githuber MD</a>, which provides a variety of features not just Mermaid, it is worth to try.
<h3>Translations</h3>
Chinese (zh_TW) by <a href="https://terryl.in/" rel="nofollow ugc">Terry L.</a>. 
Japanese (ja_JP) by <a href="https://colocal.com/" rel="nofollow ugc">Colocal</a>.
<h3>Copyright</h3>
WP Mermaid, Copyright 2020 TerryL.in 
WP Mermaid is distributed under the terms of the GNU GPL
This program is free software: you can redistribute it and/or modify 
it under the terms of the GNU General Public License as published by 
the Free Software Foundation, either version 3 of the License, or 
(at your option) any later version.
This program is distributed in the hope that it will be useful, 
but WITHOUT ANY WARRANTY; without even the implied warranty of 
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 
GNU General Public License for more details.

WP Mermaid

Generation of diagrams and flowcharts from text in a similar manner as markdown by using mermaid.js

Markdown on Save vs WP Mermaid