OpenLaunch is a Web-based content management system that integrates a broad array of services into a single, fully-featured, elegantly designed Web site. The project aims to eliminte the difficulty of integrating multiple systems into a single Web site by implementing a blog, forum, Web pages, wiki, and (coming soon) E-Commerce and support tickets. It is built around the Torpedo Framework, an open MVC framework which includes support for controllers, forms, and a large number of other very useful utilities.
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.
sfMaraePlugin is a threaded forum plugin for symfony. Current features include fully threaded categories and posts; a customizable permissions system for groups and individual users, allowing fine-grained settings for starting new topics, replying, editing, deleting, and viewing whole categories; and the ability to vote individual comments up and down.
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.
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.
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.