Fandom, previously Wikia, is a free web hosting service that uses a fork of MediaWiki as its hosting engine and is known for its wide variety of Fandom extensions. See Fandom's website or the Wikipedia article on Fandom to find out more about Fandom in general.
Fandom is a fan site where people around the world can communicate with each other and explore different TV shows, movies, video games, etc. One aspect of Fandom is that registered users can create a wiki similar to Wikipedia. Editors can edit Fandom wikis using source editor or visual editor, similar to Wikipedia and other MediaWiki wikis.
Fandom's Git repository can be accessed at github.com/wikia/app. Please note that it is an entirely separate repository from Wikimedia's official Git repository and is not affiliated with the official repo.
Some of Fandom's extensions can be found at Wikimedia's official Git repository, and their appropriate extension pages are located at Fandom extensions.
Other extensions are still located in Fandom's own Git repository, in the folder /extensions/wikia/. It is likely that most of the extensions have dependency on Nirvana (found at /includes/wikia/nirvana), the EasyTemplate class (found at /includes/wikia/ folder on Fandom's Git) and/or they might require custom database tables. Some extensions are not compatible with newer versions.
Source code comments are not as common as in the official MediaWiki, either.
- Fandom Developers — a Fandom wiki for software developers interested in Fandom's version of MediaWiki