DjZoNe

This plugins main goal was to provide the ability to any of your registered users, to invite more people to the community.
Please notice, that this plugin totaly ignores whether the registration is enabled or disabled to your blog.
<a href="https://downloads.wordpress.org/plugin/invite-friends.0.3.zip" rel="nofollow ugc">Download now!</a>
<a href="http://invite-friends.dev.rain.hu/" rel="nofollow ugc">Support</a> | 
<a href="http://invite-friends.dev.rain.hu/faq/" rel="nofollow ugc">FAQ</a> | 
<a href="http://djz.hu" rel="nofollow ugc">Author</a> 
<a href="https://www.paypal.com/cgi-bin/webscr?cmd=_donations&business=djzone@cracker.hu&item_name=Invite%20Friends%20for%20Wordpress" rel="nofollow ugc">Donate</a>
Some functions:
<ul>
<li>invitation sending</li>
<li>invitation cards limit per site</li>
<li>after activation, the user is logged in automatically</li>
<li>after activation, the user can be redirected to a custom URL</li>
<li>activation screen is using the same styles as the login screen (if you have customized login screen it will affect the activation screen as well)</li>
<li>Dashboard for custom settings Plugins > Invite friends settings</li>
<li>i18n support (localized messages)</li>
</ul>

Invite Friends

This plugin give the ability to anyone how registered to your blog, to invite more people, even if the registration is closed.

WPManiax

This plugin ads Metro style social share widget to your sidebar.
5 most popular social networks supported.
Metro Share Widget is super easy to install and configure.
More <a href="http://www.wpmaniax.com/metro-share-widget/" rel="nofollow ugc">screenshots and live sample</a> you can see on plugins’ home page
Main Features:
<ul>
<li>Easy to install and configure</li>
<li>Most popular social networks supported (Facebook, Twitter, Google Plus, LinkedIn, Reddit )</li>
<li>Fully responsive</li>
<li>Configure where to show (posts, pages, home)</li>
<li>Metro style elegant design</li>
</ul>
<h3>Feedback</h3>
http://www.wpmaniax.com/metro-share-widget/

Metro Share Widget

Add Metro style social share widget to your sidebar. 5 most popular social networks supported

Invite Friends vs Metro Share Widget