phpBB is a popular Internet forum package written in the PHP scripting language. The name “phpBB” is an abbreviation of PHP Bulletin Board. Available under the GNU General Public License, phpBB is free software.
With a large and highly customisable set of key features coupled with a standards compliant interface, phpBB will grow with, and complement your website. With millions of installations worldwide, it is no wonder phpBB is one of the most popular ways to create and support a community.
Simple Machines Forum
Simple Machines Forum — SMF in short — is a free, professional grade software package that allows you to set up your own online community within minutes.
Its powerful custom made template engine puts you in full control of the lay-out of your message board and with our unique SSI – or Server Side Includes – function you can let your forum and your website interact with each other.
SMF is written in the popular language PHP and uses a MySQL database. It is designed to provide you with all the features you need from a bulletin board while having an absolute minimal impact on the resources of the server. SMF is the next generation of forum software – and best of all it is and will always remain completely free!
Invision Power Board
Invision Power Board (abbreviated IPB, IP.Board or IP Board) is an Internet forum software produced by Invision Power Services, Inc. It is written in PHP and primarily uses MySQL as a database management system, though other database engines are available.
While Invision Power Board is a commercially sold product, there is a large modding community and many of these modifications are free. In addition, many groups offer the download or design of free and paid skins.
IceBB is a powerful, fast, free, and open-source forum solution powered by the free PHP and MySQL. IceBB scales well, no matter how many users or posts, due to its clean and efficient code. It can also be fully customized to your needs with full skin and language support. A powerful admin control center, along with easy-to-use moderation tools, allow you to easily manage all aspects of your forum.
FluxBB is a free open source forum application designed to be fast, light and user friendly.
FluxBB’s code, written in PHP, has a proven track record of stability and security. FluxBB is being actively developed and the next version 1.4 is at the beta stage.