Corrado Franco

This plugin allows one to create footnotes by using markdown notation. 
It is for footnotes only. No other markdown tag is taken into account
Example:
<pre><code>I have more [^1] to say up here.

[^1]: To say down here.
</code></pre>
If used with jetpack and enabled markdown, it only shows the buttons without modifying the text content. 
Unlike jetpack-markdown, footnotes will appear in the exact point where they have been inserted. To go back to text mode click on the footnote number.
N.B 
This plugin also works with Gutenberg. But the button only appears in the Classic Editor. 
For now with Gutenberg enter the codes directly.
<h3>Configuration</h3>
No configuration is necessary.
Considering that this plugin, like others working with “markdown”, parsing the page every time I load it, I highly recommend using a caching plugin.

Blank Footnotes

Simple plugin to show footnotes using markdown notation.

acusti

The <a href="https://wordpress.org/plugins/simple-footnotes/" rel="ugc">Simple Footnotes</a> plugin allows you to add simple, elegant footnotes on your site.
This tiny plugin makes it incredibly simple to create those footnotes, leaving nothing to teach the site’s editors (no need to explain shortcodes or special syntaxes). It adds a button to the TinyMCE editor toolbar in the second row (i.e. the “Kitchen Sink”) that users can click to open a textarea overlay where they can enter the footnote content and then insert it into the editor with the proper syntax.
<h3>Translation</h3>
<ul>
<li>French</li>
</ul>

Simple Footnotes Editor Button

Add a button to the TinyMCE editor toolbar to make it easy for users to add footnotes with the proper syntax for the Simple Footnotes plugin.

Blank Footnotes vs Simple Footnotes Editor Button