Web-based wiki software, primarily developed for use on Wikimedia properties. _(Please note that questions on how to host/configure MediaWiki are **off-topic for Web Applications.)_
MediaWiki is a popular free web-based wiki software application.
MediaWiki powers the software that runs Wikipedia, Wiktionary and Wikinews and is one of the most popular software for deploying Wiki-sites.
(Please note that questions on hosting/configuring MediaWiki are off-topic for Web Applications.)