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.
DBOX is a free communication package for ISPs. It supports a large number of message formats such as RFC/UUCP, ZConnect, Janus/Janus2, Alphabox, and GSbox. It is designed for large installations and includes a WWW package with an email/HTML gateway, an HTML online shop, support for POP3/IMAP4, and personal homepages with HTTP/FTP upload.
Devalot is a social networking application centered around software projects. It connects the user community with the development community and encourages participation and communication. It includes all the features you've come to expect in modern Web-based applications such as tagging, comments, and a wiki, as well as features you'd expect in project tracking software such as ticketing. It has features similar to some of those found in Trac, Collaboa, GForge, Mephisto, and Typo.
This program hopes to become a viable MS Sharepoint clone. It is basically a Web interface to a document repository (Frontpage Web), but with many other features. It depends on Frontpage extensions for remote authoring; otherwise it is independent. It includes a forum, calendar, event tracking, announcements, tasks, file check in/check out, user management, email, and more.
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.
The Faq-O-Matic is a CGI-based system that automates the process of maintaining a FAQ (or Frequently Asked Questions list). It allows visitors to your FAQ to take part in keeping it up-to-date. A permission system also makes it useful as a help-desk application, bug-tracking database, or documentation system.