MediaWiki is free software that works by installing it on a server. It has a GNU General Public License (GPL). It uses PHP to process pages that are saved in a database that can be MySQL, MariaDB, or others.
Pages use HTML and CSS to display content and make it easy to modify. Images and other types of multimedia are also saved.
The pages are saved in the database, but the versions of them also, so changes can be easily reversed.
It is a wiki software that is a virtual community that has pages which are edited by the users themselves using only a web browser.
It is server software, it can be open on Internet or on an internal LAN
It is free software
On this page you can consult a "cheat sheet" that has basic formatting instructions.