Apptha Social Login is an easy to install extension that is user friendly and have chained up with many different languages with an alternate option for default joomla registration and login form. Completely customizable it performs seamless. User can login with their existing social networking site in few clicks. It is easy and efficient, since the user need not remember the password for the particular site.
Demo:
http://www.apptha.com/joomla/social-login