Beherit

Sends an simply email notification to the comment author, when someone replies to his comment. No configuration, support WordPress translation process.

Simple Comment Notification

Sends an simply email notification to the comment author, when someone replies to his comment.

kingjeffrey

From the authors of <a href="https://wordpress.org/extend/plugins/wp-typography/" rel="ugc">wp-Typography</a> comes wp-AuthorComment, allowing you to uniquely style post author’s comments.
View the <a href="http://kingdesk.com/projects/wp-authorcomment/" title="wp-AuthorComment Homepage" rel="nofollow ugc">wp-AuthorComment homepage</a> for more information.

wp-AuthorComment

Uniquely style the post author's comments.

Simple Comment Notification vs wp-AuthorComment