Acity
Acity 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 totally stable. Acity 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 themes, forums and administrators for each group. It runs on any OS that have Apache, mod_perl and a SQL server.