Web-based discussion forums (non-nntp based, with or without bidirectional
mailing list access). Try these first.
Zorum "is an easy to install Web-based forum, message board, or bulletin board, based on mysql, php4. Some of its main features include both threaded and linear views, personalization, moderated forums, and styled skins."
KOM2000 is a web-based discussion forum that also provides nntp access.
by Lyris Technologies, Inc. The Multiview module makes it so that the mailing lists can be read and posted to via newsreading software.
WebBoard by O'Reilly for 95/98/NT does web boards and mailing lists. Users can read/post via nntp if they wish. (purchase)
WebCrossing is a "community" package, meaning it provides a web site and communication packages for virtual communities. Web, Webmail, POP3/IMAP/SMTP, web-based and NNTP forums, and can run mailing lists.
Forum News Gateway from the Math Forum is no longer supported. Their new tool is Epigone, which does newsgroups, mailing lists, and web discussions. Interested groups of mathematicians or mathematics educators may contact them directly for consideration of Forum discussion group software use and hosting. Interested groups of stakeholders (of WebCT) in other academic fields may contact email@example.com
Spellchecker.net provides tools for web-based systems to allow users to spellcheck their work.