WP Private Comment Notes will let WordPress admins/moderators add and manage private notes for each comment left through the WordPress commenting system. Additionally, each note can be shared with the user who left the original comment.
Comment notes can come in handy when managing popular blogs. WP Private Comment Notes serves as a “note to self” tool for comment moderators, or a private method of communication with the commenter.
Credits
Thanks to Ana Nirwana for the cool little message icon.