Marc Tönsing

Ipstenu (Mika Epstein)

This plugin displays the most basic of quicktag buttons on your comment forms, using the Quicktag API built into WordPress (as of 3.3). No jQuery needed.
Contribute on <a href="https://github.com/mtoensing/marctv-quicktags" rel="nofollow ugc">GitHub</a>.

Simple Comment Quicktags

Simple and clean

Make commenting easier with bold, italic, add link and quote buttons on top of the form.

David Klhufek

This simple plugin adds useful buttons to the native WordPress HTML editor (Classic Editor).
Currently adds: 
h1, h2, h3, h4, h5, span, hr, nbsp, mox
The “mox” button adds a nice responsive CSS class which you can use to highlight pictures or other elements in your posts.
Note: This plugin works only with the Classic Editor. It does not support the new Gutenberg (Block Editor).
<h3>Compatibility</h3>
<ul>
<li>Requires the Classic Editor to be active. </li>
<li>Designed specifically for the HTML mode of the editor.</li>
</ul>

Quicktags for WP

This simple plugin adds useful buttons to the native WordPress HTML editor.

Simple Comment Quicktags vs Quicktags for WP