UseBB is a PHP/MySQL forum package. Unlike other popular forum systems, it does not strive to have as many features as possible, but to be one of the easiest and most usable forum packages, limiting the basic feature set to only the essential. It is an ideal solution for small to medium-sized Web sites which require an easy to use forum package without the bloat, that produces standards compliant output, and is secure and easily configurable.
fp.board is a bulletin board software solution designed to both implement features of proprietary non-free solutions and provide exceptional security. It supports features such as a built in Markdown Engine along with BBCode, an advanced Ban Control Panel (modeled after IRC, with Account Exceptions and CIDR based IP bans), DNS Blacklist checks, checks against the StopForumSpam databases, and more. It has no issues with the Suhosin Patches, and is developed on a server that supports Suhosin.
FluxBB is a fast, light, user-friendly forum application for Web sites. It was originally based on PunBB and supports UTF-8, XHTML, and internationalization, and leaves out some of the less than essential features of other forums without sacrificing essential functionality or usability.