vBulletin - Build a community website with the leading forum software, vBulletin 5 Connect, or in the cloud on vB Cloud!
Google Groups - Google Groups allows you to create and participate in online forums and email-based groups with a rich experience for community conversations.
Discourse - Discourse is an open source discussion platform built for the next decade of the Internet.
DownToMeet - DownToMeet is a platform to organize, find, and attend group events.
XenForo - Intuitive. Social. Engaging. Fast. XenForo brings a fresh outlook to forum software.
Mighty Networks - Mighty Networks enables entrepreneurs, organizations, and companies to create and grow a community-powered brand.