Agora is a web-based, threaded discussion tool. It's *fast*, very intuitive to use, was beta-tested by more than a hundred people, and is now totaly stable. Agora remembers each user's preferences, and allows unread-only browsing, like a usenet-news system. It offers the ability to manage several different groups, with different forums and administrators for each group. Version 1.3x has a "skin" system which allow each users to have his own colors/fonts/background.
Agora runs on any OS that have Apache, Perl, and a SQL server. It's compatible with mod_perl accelerator, which is highly recommended for maximum performance.
A demo version is available (2000-11-21). You can subscribe here.
Maybe, the screenshots and the FAQ tell more than I can in a few words...
The SourceForge home for Acity is http://sourceforge.net/project/?group_id=1685