Bitrix24 - Bitrix24 is a free (for small businesses) social enterprise platform. It is a united work space which handles the many aspects of daily operations and tasks. Create your own social intranet in minutes!
SocialEngine - Socialengine PHP: Elevating Your Online Community Experience.
LinkedIn Premium - LinkedIn is a social network helping brands and professionals to connect, identify sales prospects, hire talent, and promote their business.
mooSocial - mooSocial is the best social network script to create a niche community or social site.
Salesforce Chatter - Salesforce Chatter provides a suite of collaboration features to any application built on Force.com.
JomSocial - Open Source Social Networking Software. Award winning open source community software by JomSocial. This social networking software is widely used by many Joomla users.