WordPress is a free and open-source content management system based on PHP and MySQL. It allows users to install and switch between themes to change the look and functionality of a website without altering content. Over 38,500 plugins are available to extend WordPress features and tailor sites to specific needs, such as search engine optimization or client portals. Native mobile applications exist for many platforms to add and moderate content on the go with limited options. WordPress also offers integrated link management, clean permalinks, post tagging and formatting, and trackback/pingback link displays.