phpBB is an open source bulletin board software package. It is a web-based application written in PHP and is used to create and manage a variety of discussion forums and bulletin boards. phpBB allows users to create topics, reply to existing topics, attach files, and edit posts. It also has user-friendly features such as a search engine, private messaging, user groups, a user ranking system, custom themes and styles, and an extensive plugin system that allows users to customize their forums with a variety of additional features and functions. phpBB is a great solution for businesses and enterprises that need to create a community and get their customers engaged with discussions and conversations.
It is more of an online messenger than a cms forum.