wiki.gg
wiki.gg is a free wiki hosting service created by video game publishing company, Freedom Games. It is focused mostly on video game wikis, and uses MediaWiki version 1.43.1 as its hosting engine. wiki.gg derives income from advertisements.
Extensions
editwiki.gg can install MediaWiki extensions, by request of the respective wiki admin. See the page regarding extensions on the wiki.gg Support Wiki for a full list of all available extensions alongside a guide on requesting them.
Alongside that, there are also Category:Extensions by wiki.gg, available as free open source software.
Code
editwiki.gg uses open source code, and hosts it on GitHub.