Wiki software (also known as a wiki engine or wiki application) is collaborative software that runs a wiki, which allows users to create and collaboratively edit "pages" or entries via a web browser. A wiki system is usually a web application that runs on one or more web servers. The content, including all current and previous revisions, is usually stored in either a file system or a database. Wikis are a type of web content management system, and the most commonly supported off-the-shelf software that web hosting facilities offer. There are currently dozens of actively maintained wiki engines, in a variety of programming languages, including both open source and proprietary applications. These vary widely in their platform support, their support for natural language characters and conventions, and in their assumptions about technical versus social control of editing.