nickgrossman

Enable commenting on your posts via Twitter.
Posts will get a “Discuss on Twitter” button, which will prompt visitors to reply to the original tweet about the post, as well as a “View Discussions” button which will link to existing tweets about the post.
Each new post will be auto-tweeted (requires the <a href="https://wordpress.org/plugins/wp-to-twitter/" rel="ugc">WP to Twitter</a> plugin and a <a href="https://developer.twitter.com/" rel="nofollow ugc">Twitter Developer account</a>).

Discuss on Twitter

Jeff Waugh

Automagically link Twitterish “@name:” replies in comments.
Note: It hasn’t been tested on versions earlier than 2.1, but may very well work.

@reply

Automagically link Twitterish "@name:" replies in comments.

Discuss on Twitter vs @reply