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.
Shapado is a multi-topic and multi-language question-and-answer Web site service à la StackOverFlow where users can vote on questions and answers and receive karma. Unlike StackOverFlow, people can ask questions on various topic by picking a category (science, programming, business, politics, etc.). It is also possible to subscribe to categories or groups of categories.
Sijio is a fast, high performance, easy to use and fully customizable PHP community script. It is equipped with all necessary professional tools and features to run a full fledged community site. Features include blogs, events, a forum, a gallery, polls, page management, user management, and RSS feeds, customizable Smarty powered templates, WYSIWYG editing of any content, easy picture upload, an unlimited number of attachments, and more. It is completely SEO friendly.
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.
TinyIB is a lightweight PHP image board which emulates the functionality of 4chan. If you use MySQL or SQLite, you can use it to create an efficient setup able to handle large amounts of traffic. If you don't use a database, it can store posts as text files for a portable setup capable of running on virtually any PHP host.
MyBestBB is a full-featured forum based on punBB. It adds many features, modifications, and themes to the default punBB, including RSS feeds, UTF-8, XHTML 1.0 strict compliance, sub-forums, PMs, attachments, rewrite rules, the ability for an admin to move posts, easy smilies, easy polls, many improved themes, announcements and sticky topics, an activity barometer, a URL rewriting module, and much more.
Nearforums is a lightweight powerful discussion forum that can be installed within minutes on Linux or Windows servers with MySQL or MS SQL database servers. It includes great features like sign-in with Facebook/Twitter, navigation with tags, full Web administration, built-in search engine, RSS feeds, and accessible HTML. It is SEO friendly.