Simple Machines Forum
Simple Machines offers free open source software such as SMF, the powerful and easy to use community forum written in PHP. Start interesting discussions on your website!
17 Alternatives To Simple Machines Forum
ArmorForums
Platform for creating free private forums on a subdomain and cloud hosted software developed and maintained by ArmorForums.
Invision Community
Invision Community is a flexible, integrated set of apps for building communities on the web.
vBulletin
Build a community website with the leading forum software, vBulletin 5 Connect, or in the cloud on vB Cloud!