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> 
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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.

ircf

Disable email requirement for user registering/editing.
This plugin hooks the following WordPress functions :
<ul>
<li>wp_user_insert()</li>
<li>wp_user_update()</li>
<li>Admin site email validation</li>
<li>Admin site profile editor</li>
</ul>

Email not required

Disable email requirement for user registering/editing.

Invite Friends vs Email not required