MyBB, also known as MyBBoard or MyBulletinBoard, is a powerful, efficient, and free forum package, developed using PHP and MySQL.
MyBB has been designed with both the end user (you and your subscribers) and the people who staff your message board in mind. Full control over your discussion system is presented right at your fingertips, from the ability to have multiple themes to the ultimate customization of your forums using the template system and plugins.
MyBB also presents a wide variety of useful features that make it unique. Most important of all, MyBB is completely free.