Agora is a Web-based, threaded discussion tool, similar to Usenet newsgroups. Agora remembers each user's preferences, and allows threaded, unread-only browsing. It offers the ability to manage several different groups, with different themes, forums, and administrators for each group. Agora offers a basic Web-based ICQ client, as well as a Web-based notes system.
CGIForum is a highly configurable template-based discussion board. It supports expandable/collapsible threads of unlimited depth, name registration with password encryption, multiple sections from within a single script, previewing, searching, and marking of new entries. It also lets you specify date-ranges to limit the number of displayed entries. The included administration script lets you change, delete, and restore entries at any time.
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.
WCN:Talk (originally called "FutureForum") is a Web discussion forum written in Perl and MySQL. It has many options, including message selection and sorting on the top index page. It also has collapsible branches, a menu that toggles between 'no menu', 'simple', and 'advanced' modes, full text search capability, the ability to send email to the admin and original poster, and many other features. It includes password protection, HTML templates, file uploads, message subscription, multiple discussion sections, and a lot more.