7th BBS
   A modular Bulletin Board System based on PHP 5 and MySQL 4+. [Open source, GPL]
   http://www.7thbbs.com/

Bestweb
   Usenet style threaded discussion, multiple forums, multiple languages, automatic archiving, printable pages, and message voting.
   http://bestweb.ca/

DCForum+
   A PHP/MySQL implementation of DCForum web discussion program. [Commercial]
   http://www.dcscripts.com/dcforump.shtml

FUD Forum
   Very feature-rich PHP forum system with MySQL/PostgreSQL backend.
   http://fudforum.org/forum/

FunkBoard
   A multi-thread customisablebulletin board messaging system. It uses PHP and either MySQL or PostgreSQL database. [Freeware]
   http://www.funkboard.co.uk/

IbPhp
   Ikonboard's PHP version. It supports all CGI version's features and it's free. A free registration is required to download the script.
   http://www.ikonboard.com/

IceBB
   Open-source forum software in PHP.
   http://icebb.net/

MBoard
   A simple message board for those who don't want or need large forums. Supports smileys, e-mail notification and more. [Freeware]
   http://www.phpjunkyard.com/php-message-board.php

MercuryBoard
   Bulletin board written in object-oriented PHP4 with a MySQL database backend.
   http://www.mercuryboard.com/

Oneiric Bulletin Board
   Oneiric is a free (GNU/GPL) PHP Bulletin Board with a mySQL backend.
   http://www.oneiric.de/board/

OvBB
   A light-weight and fast bulletin board system that mimics vBulletin 2 in both look and behavior while incorporating new features and functionality. [Open source, MIT]
   http://www.ovbb.org/

Oxygen
   A highly customisable open-source web-based bulletin board that requires PHP4, a mySQL database.
   http://www.o2php.com/

PHP/XML Forum
   A free thread-oriented, XML-based news forum. No database required.
   http://outer-court.com/tech/forum.htm

Phorum
   A free threaded, web-based bulletin board system written in PHP with a variety of backend database option available.
   http://phorum.org/

Prattle
   A message board system implementing a clean linear model. [Open source, GPL]
   http://prattle.sourceforge.net/

ProBB
   ProBB is a web bulletin board written in PHP and backed by several databases, including MySQL, MsSQL, and PostgreSQL.
   http://www.halfstrike.com/probb/

PunBB
   News, information, downloads, newsletter subscription, international support, hosting and forums for the lightweight discussion board. [Open source, GPL]
   http://punbb.org/

SEO-Board
   A fast, and search engine friendly forum software written in PHP/MySQL. [Open source]
   http://www.seo-board.com

SMF
   A community software package with themes, fast message database, secure file-attaching system, and mod installation manager. [Freeware]
   http://www.simplemachines.org/

SkaidonDesigns
   Template designer for phpBB, vBulletin, IPB software.
   http://www.skaidon.co.uk

SowiBB
   Forum software written in PHP with a MySQL backend.
   http://sourceforge.net/projects/sowibb

Supermod
   A PHP forum software to a higher level YABBSE based concept radically modified and customized for free.
   http://www.supermod.org/

Transverse Styles
   Provides Invision Power Board skins and vBulletin styles. All skins and styles are packaged with fixed and fluid configurations. [Commercial]
   http://www.transversestyles.com/

UBBThreads
   Threaded or linear viewing of posts, address books, CSS compatible, session or cookie based, moderators, multi-language support, private forums, profanity filter, and user pictures. [Commercial]
   http://www.ubbcentral.com/

Unclassified NewsBoard
   Unicode-supporting PHP/MySQL forum software that produces standard XHTML and CSS. [Open source, GPL]
   http://newsboard.unclassified.de/

UseBB
   A PHP/MySQL bulletin board package designed for small to medium sized web sites. [Open source, GPL]
   http://www.usebb.net/

Vanilla
   PHP/MySQL forum software with multilingual support and more than 100 plug-ins. [Open source, GPL]
   http://getvanilla.com/

W-Agora
   Free forum written in PHP. It has also a guestbook, a download area, a photo gallery and a news publisher feature. It uses MySql as database.
   http://www.w-agora.net/

WMForum
   A very simple discussion board program written in PHP. It doesn't use any SQL database.
   http://wmforum.lehed.com/

WSN Forum
   Fully customizable, extensible and translateable PHP/MySQL forum script. [Commercial]
   http://www.wsnforum.com

WiForums
   Interoperable (vBulletin, phpBB2 and IPB) Web/WAP Discussion Forums for Cell phones, PDAs and other handheld devices.
   http://www.wiforums.net

WowBB
   WowBB offers features such as auto install/upgrade, a WYSIWYG editor with integrated spell-checker, auto time zone detection and smart caching. Requires PHP and MySQL.
   http://www.wowbb.com

XMB
   PHP/MySQL forum software that supports themes, BB code, and instant messaging. [Open source, GPL]
   http://www.xmbforum.com

Xsorbit
   Free forums and professional message board and forum software for personal or business use.
   http://www.xsorbit.com

YaBB SE
   A PHP/MySQL port of Yet another Bulletin Board (YaBB) 1 Gold (see above).
   http://www.yabbse.org

aterr
   An open-source, web-based, threaded forum system written in PHP, supporting nested posts and forums.
   http://chimaera.starglade.org/aterr/

bSpeak Threaded Messageboard
   A PHP and MySQL based messageboard software. [Commercial]
   http://www.26thavenue.com/index.php?action=products.bspeak

bbPress
   Template-driven PHP/MySQL forum software developed by the creators of WordPress. [Open source, GPL]
   http://bbpress.org/

ccForum
   A simple, easy to use message board system. It supports single or multiple forums, user registration and anonymous posting, and forum administrators. ccForum is written in PHP and is based on a MySQL database. [Open source, GPL]
   http://ccforum.sourceforge.net/

ezPhpForum
   A simple to use PHP forum package.
   http://www.ezphpforum.com

miniBB
   Small, fast and free discussion board system written in PHP, can be based on any database supported by PHP (including mySQL and PostgreSQL).
   http://www.minibb.net/

myBB
   Coded in PHP and backed by mySQL. Free
   http://www.mybboard.com/

phpNet
   A feature enriched PHP/MySQL message board.
   http://php-net.net/

tribbyBoard
   A free threaded message board script written in PHP with a MySQL backend.
   http://www.tribby.com/board/