SocialEngine - Socialengine PHP: Elevating Your Online Community Experience.
vBulletin - Build a community website with the leading forum software, vBulletin 5 Connect, or in the cloud on vB Cloud!
mooSocial - mooSocial is the best social network script to create a niche community or social site.
Discourse - Discourse is an open source discussion platform built for the next decade of the Internet.
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.
XenForo - Intuitive. Social. Engaging. Fast. XenForo brings a fresh outlook to forum software.