vBulletin - Build a community website with the leading forum software, vBulletin 5 Connect, or in the cloud on vB Cloud!
Mighty Networks - Mighty Networks enables entrepreneurs, organizations, and companies to create and grow a community-powered brand.
Discourse - Discourse is an open source discussion platform built for the next decade of the Internet.
Bigtent - BigTent is a web-based organization and communication portal for groups.
XenForo - Intuitive. Social. Engaging. Fast. XenForo brings a fresh outlook to forum software.
Nabble - Nabble is a forum software that are embeddable and fully customizable with scripting language.