First versions of Absolute Comments implemented several features that are now, out of the box, part of WordPress.
Absolute Comments now simply adds a “Reply” link into comment notification emails, prefills the comment reply with the commenter’s name, and adds a few cute icons.
There’s no option or settings: just activate and forget it’s even a plugin.
Official page: <a href="http://planetozh.com/blog/my-projects/absolute-comments-manager-instant-reply/" title="Absolute Comments" rel="nofollow ugc">Absolute Comments</a>
Tip: To keep track of this plugin’s evolution and features, you are advised to subscribe to the <a href="http://planetozh.com/exit/feed" rel="nofollow ugc">author’s feed</a> or follow him on Twitter: <a href="http://twitter.com/ozh" rel="nofollow ugc">@ozh</a>

Ozh' Absolute Comments

Reply to comments from email notification

Doodlebee

Simple plugin to show/hide comment replies, rather than have them all listed. An options page makes it really easy to change different parts of your comment calls.
<h4>Features</h4>
This keeps the default “<a href="https://codex.wordpress.org/Function_Reference/wp_list_comments" rel="nofollow ugc"><code>wp_list_comments()</code></a>” features. A clickable span that triggers the action to expand the replies is also added.
New features are including easing options, as well as allowing images. An options page has been added for further customizations, making it even easier to use.
<h3>Other Info</h3>
<h4>Known Issues</h4>
None at this time.
<a href="http://brassblogs.com/contact" rel="nofollow ugc">Contact Shelly</a>
Given that this is free, I offer limited support. If you have issues with the plugin working I will do whatever I can to help you fix the issue, but when it comes to customization, I’m in limited supply. I’ll do what I can, but no guarantees. This is your standard “as is” application. In all honesty, ask customization questions in the forums – if I can’t help, perhaps someone else can. (If you want to hire me to customize it, that’s another story – feel free to contact me to do so!)
PLEASE NOTE that the WordPress support system DOES NOT notify me when someone leaves a support question. It requires me to come back and check manually to see if anyone has had an issue. Sometimes, I don’t get to do that for a while. If you left a support request on the forums, and it’s been at least a week since you left it with no response, please drop me an email to let me know so I can attempt to help you out. I’m pretty good at helping out – but I’m not so good at coming to check the forums – especially when I’m busy with client work.

jQuery Comment Replies

Make your multi-level comment replies show on demand with a slick jQuery slideToggle() action.

Ozh' Absolute Comments vs jQuery Comment Replies