MediaWiki is open source server-based software written in PHP, originally for use on Wikipedia, licensed under the GNU General Public License (GPL). MediaWiki engine is collaborative editing software used by many sites including Wikipedia, Wiktionary, wikiHow, WikiLeaks and Wikimedia Commons. It's designed to run on a large server farm. The Pages use MediaWiki's wikitext format, so that users without knowledge of XHTML or CSS can edit them easily. When a user submits an edit to a page, MediaWiki writes it to the database, but without deleting the previous versions of the page. MediaWiki can manage image and multimedia files, too, which are stored in the filesystem. MediaWiki can be easily coupled with Squid proxy server software and achieves scalability through multiple layers of caching and database replication. MediaWiki uses Apache web server for delivering web pages, the relational database management system MySQL as a database backend for storing the content, and the scripting language PHP for the application logic that combines together these components.