Flarum - Flarum is the next-generation forum software that makes online discussion fun. It's simple, fast, and free.
Mighty Networks - Mighty Networks enables entrepreneurs, organizations, and companies to create and grow a community-powered brand.
XenForo - Intuitive. Social. Engaging. Fast. XenForo brings a fresh outlook to forum software.
Bigtent - BigTent is a web-based organization and communication portal for groups.
Discourse - Discourse is an open source discussion platform built for the next decade of the Internet.
Nabble - Nabble is a forum software that are embeddable and fully customizable with scripting language.