MyBB

MyBB, formerly MyBBoard and originally MyBulletinBoard, is a free and open-source forum software developed by the MyBB Group. It is written in PHP, supports MariaDB, MySQL, PostgreSQL and SQLite as database systems and, in addition, has database failover support. It is available in multiple languages and is licensed under the LGPL. The software allows users to facilitate community driven interaction through a MyBB instance.

Excerpt from Wikipedia: MyBB. Content available under CC-BY-SA 4.0.