Phorum is a web based message board written in PHP. Phorum is
designed with high-availability and visitor ease of use in mind.
Features such as mailing list integration, easy customization
and simple installation make Phorum a powerful add-on to any
website."

With advanced moderation features, built-in newsletter
distribution, private messaging and full-text search, Phorum is
a worthy alternative to other commercial scripts that's well
worth investigating.

Script Name: Phorum (Opensource)
URL: http://www.phorum.org