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

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

MarkdownBar vs WP Mermaid