Gnew is a simple content management system. It is fully customizable using a template system, and supports multiple languages. It features easy installation, a simple but complete administration section, multi-level categories, article management, news management with an advanced comments system, poll management, user management, a forum, search engine, RSS feed generation, BBCode and HTML support, emoticons, and more.
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.