BuddyPress - WordPress social networking in a box.
Ultimate Member - The easiest way to create powerful online communities and beautiful user profiles with WordPress.
MemberPress - Easy to use WordPress Membership Plugin. Powerful Membership Software seamlessly integrates with WordPress, Stripe, PayPal and Authorize.net.
bbPress - bbPress is forum software with a twist from the creators of WordPress.
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.
HumHub - HumHub is a free social network software and framework built to give you the tools to make teamwork easy and successful.