This is the Vikinghammer Tweet plugin.
You can set it up to post tweets based on new posts or comments to your blog. This requires that you enter your Twitter credentials.

Vikinghammer Tweet

Send a tweet for any new post or comment to your blog.

yakuphan

Comment Approved Notifier sends an e-mail to your commenters when you approve their comments. It is a very simple plugin. There are no settings, options. It starts to work when you activate it.
<h4>Read Please</h4>
If you upgraded to WP 2.7 or WP 2.8, please, update v1.1 to v2.1 
It requires at least 2.7. If you use WP 2.6.5, please use version 1.1
Thanks!

Comment Approved Notifier

https://wordpress.org/plugins/comment-approved-notifier-extended/
Updated version of this plugin. forked.

Updated

The plugin sends an e-mail to your commenters when you approve their comments.

Vikinghammer Tweet vs Comment Approved Notifier