Skysa

Simply set the Twitter account you want users to follow; then, when they click the Twitter Follow button at the bottom of your site, they will start following your account on Twitter. You can optionally set to display your current followers count next to the Twitter follow button and also the language of the Twitter follow button text.
http://www.youtube.com/watch?v=Zj1uGXX2xrk&hd=1 
<a href="https://wordpress.org/extend/plugins/tags/skysa-apps" rel="ugc">More Skysa App plugins</a> -|||- <a href="https://wordpress.org/extend/plugins/skysa-official/" rel="ugc">Skysa App Bar Integration plugin</a>

Skysa Twitter Follow App

Allows your site visitors to follow your twitter account with one click, without leaving your sitet.

Matthias Pfefferle

julien51

This widget adds a <a href="http://www.subtome.com/" rel="nofollow ugc">SubToMe</a> button to your WordPress blog. This button allows your readers to follow your blog using their favorite applications.
If the user clicks the button, then, it will load an external iframe with JavaScript. The iframe will show the user the list of their favorite subscription tools. Once they pick one, they’re redirect to it with your blog information.
The user information is stored in the browser, but is only accessible on the domain <code>subtome.com</code>, which is why we have to load the iframe.
No data is ever “leaked”. The whole <a href="https://github.com/superfeedr/subtome" rel="nofollow ugc">SubToMe code</a> is open source. Feel free to check it out by yourself.
<h3>Credits</h3>
<a href="https://github.com/tommcfarlin/WordPress-Widget-Boilerplate" rel="nofollow ugc">WordPress Widget Boilerplate</a>, <a href="http://notizblog.org/" rel="nofollow ugc">Matthias Pfefferle</a> for his precious help, mostly with version 1.3!

SubToMe

This widget adds a SubToMe button to your blog and allows people to subscribe to your content in one click.

Skysa Twitter Follow App vs SubToMe