Joomla is a very popular and user friendly free and open source content management system, based on PHP that allows you to easily create and manage a dynamic web site. It is used all over the world to power everything from simple, personal web sites to complex corporate web applications. Joomla has many extensions suitable for different types of websites like social networking web sites, business portals, blogs, e-commerce web sites etc. that will provide the functionality that you may need, without having to build from scratch.