olivierognn

With this plugin you can use the shortcode [twitter-author] to add a nice preview of the author’s twitter profile in your post. The only requirement is that the author has indicated his twitter nickname in the user management page of WordPress.

twitter-Author-follow

This plugin helps you to show the author twitter profile in your posts using the shortcode [twitter-author]

antonpug

This plugin adds a customizable Better Follow Button at bottom right corner of your Jetpack-powered WordPress.org site.
The plugins integrates with the built in subscription manager of the Jetpack Plugin to collect the email of the subscriber and handle distribution of new posts via email.
NOTE: This plugin requires the Jetpack plugin to be installed & activated
For further information visit the plugin website.

Better Follow Button for Jetpack

Adds a floating subscription button (like on WordPress.com sites) to Jetpack-powered WordPress.org sites.

twitter-Author-follow vs Better Follow Button for Jetpack