Zane Matthew

This plugin places a comment form similar to Facebook, only displaying a single line textarea, which submits when the user presses “enter/return” on their keyboard.
<h4>Features</h4>
<ul>
<li>Single line textarea</li>
<li>Auto expanding textarea</li>
<li>AJAX submitted comments</li>
<li>AJAX loaded comments</li>
<li>Admin settings for additional styling</li>
</ul>

Inline Ajax Comments

Displays a single line textarea for entering comments, users can press "enter/return", and comments are loaded and submitted via AJAX.

scribu

Jotschi

Front-end Editor is a plugin that lets you make changes to your content directly from your site. No need to load the admin backend just to correct a typo.
It makes the same <a href="https://codex.wordpress.org/Roles_and_Capabilities" rel="nofollow ugc">capability</a> checks, so that if a user isn’t allowed to edit something in wp-admin, they aren’t allowed to edit it in the front-end either.
You can edit posts, pages, custom post types, comments, widgets and many <a href="http://github.com/scribu/wp-front-end-editor/wiki/List-of-editable-elements" rel="nofollow ugc">more elements</a>.
Goals:
<ul>
<li>save as many trips to the backend as possible</li>
<li>compatible with any theme, out of the box</li>
<li>light and fast</li>
</ul>
Support and development:
<a href="https://wordpress.org/support/plugin/front-end-editor" rel="ugc">Support</a> is handled by the lovely <a href="https://wordpress.org/support/profile/designsimply" rel="ugc">designsimply</a>.
I am not developing the plugin anymore; only applying the patches that other people send via <a href="https://github.com/scribu/wp-front-end-editor/" rel="nofollow ugc">Github</a>.
Credits:
<ul>
<li><a href="http://aloha-editor.org" rel="nofollow ugc">Aloha Editor</a> for the fantastic WYSIWYG editing component</li>
</ul>
Links: <a href="http://github.com/scribu/wp-front-end-editor/wiki" rel="nofollow ugc">Documentation</a> | <a href="http://scribu.net/wordpress/front-end-editor" rel="nofollow ugc">Plugin News</a> | <a href="http://scribu.net" rel="nofollow ugc">Author’s Site</a>

Front-end Editor

Edit content inline, without going to the admin area.

Inline Ajax Comments vs Front-end Editor