One of the primary difficulties a web site faces is managing content. This can include enabling multiple user levels access for content development and editing, establishing staging and production areas of a site, all while maintaining integrity of the design and application levels.
There is substantial open source development in content management systems (CMS) and there is of course a portal and organization devoted to aggregating access to the best open source systems available.
OSCOM – The international association for Open Source Content Management, brings together developers and users to improve and promote open source CMS. Be sure to see their extensive matrix of systems available.