BuddyPress - WordPress social networking in a box.
SocialEngine - Socialengine PHP: Elevating Your Online Community Experience.
Ultimate Member - The easiest way to create powerful online communities and beautiful user profiles with WordPress.
mooSocial - mooSocial is the best social network script to create a niche community or social site.
MemberPress - Easy to use WordPress Membership Plugin. Powerful Membership Software seamlessly integrates with WordPress, Stripe, PayPal and Authorize.net.
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.