FUDforum is a templatable forum with i18n support based on PHP and either MySQL, Oracle, PostgreSQL, or SQLite. It features a user/group management system, a multi-lingual spell checker, both flat and thread message views, a private messaging system with multi-user forwarding capabilities, poll file attachments, and much more. It is an extremely fast and scalable forum that can fulfil the needs of both small and large forum operators.
phpBB is a UBB-style dissussion board written in PHP backended by a MySQL database. It includes features such as posting/replying/editing messages, private messages, private forums, user and anonymous posting, robust theming, user ranking by posts or by special, admin definable, ranks, and much more.
Citadel is an advanced messaging and collaboration system for groupware and BBS applications. Users can connect to Citadel using any telnet, WWW, or client software. Among the features supported are public and private message bases (rooms), electronic mail, real-time chat, paging, shared calendaring, address books, mailing lists, and more. Unlike other collaboration servers, Citadel provides its own data stores and is therefore extremely easy to install; you don't have to "bring your own" email and database because they're built in. The server is multithreaded and scalable. In addition, SMTP, IMAP, and POP3 servers are built-in for easy connection to Internet mail. Citadel is both robust and mature; it has been in production since 1987.
aGNeS is a solid BBS system from Vestris Inc. aGNeS allows threaded discussions, article searching, archiving, thread expanding and collapsing, etc. It allows to setup as many web boards as desired with totally different layout , using one CGI. The look and feel of your forum can be just whatever you like using template pages. aGNeS is web-administrable. There are tons of features and options.
PunBB is a fast and lightweight discussion board. Its primary goal is to be a faster, smaller, and less graphic alternative to otherwise excellent discussion boards like phpBB, Invision Power Board, and vBulletin. It has fewer features than many other discussion boards, but is generally faster and outputs smaller pages.
miniBB is a flat, linear, highly customizable BB. It features MySQL, PostgreSQL, and MSSQL support, table name definitions, color skins, language packs, HTML templates, access control, smilies, search, basic BB codes, member titles and ranks, moderators, email notification, statistics, encrypted cookie logging, IP and user ID tracking and bans, spam protection, "sticky" topics, a powerful admin panel, and more.
PHPX is a Web portal system, blog, Content Management System (CMS), forum, and more. It is designed to allow everyone to be able to have feature-rich, interactive websites even if you do not know a bit of programming. Some key features include fully-integrated forums, downloads, an image gallery with slideshow and auto-thumbnailing, support ticket system, a GUI interface for Web page content management, news with topics and instances, and a whole lot more. It allows you to fully customize the look of your site.
Zorum is an easy-to-install Web-based forum, message board, or bulletin board. It requires a MySQL database, and the PHP4 script module. Features include an easy Web-based install, embedded administration, a style manager, personalization, threaded and linear views, moderators, password reminder, post blocking rules, bb code, mark unread messages, and much more.
OPT (Outreach Project Tool) is a PHP general-purpose virtual commonplace for customers and developers to collaborate in developing projects. The system provides documents archive, e-mail archive, request tracker, task management, knowledge base, news administration, newsletter support, and a lot of other features (some project-based, some system-based).