Dekisugi

This “Insert Footnote” plugin add any text or HTML code at the bottom of all post contents. If you are tired of text-insertion plugins that is just too bulky and complicated, this simple and light plugin is ideal for you. Javascripts such as adsense codes can also be added.
The nice thing about this plugin is you don’t get extra blank lines above and below your custom footnote, therefore looks nicer on your posts. Visit <a href="http://dev.coziplace.com/free-wordpress-plugins/insert-footnote" rel="nofollow ugc">Official</a> page.

Insert Footnote

This plugin add custom texts/HTMLs/scripts below all post contents. This plugin is so light.

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.

Insert Footnote vs Blank Footnotes