Wikipedia
MediaWiki is a free and open-source wiki application. Originally developed by Magnus Manske and improved by Lee Daniel Crocker, it runs on many websites, including Wikipedia, Wiktionary and Wikimedia Commons. It is written in the PHP programming language and stores the contents into a database. Like WordPress, which is based on a similar licensing & architecture, it has become the dominant software in its category.
The first version of the software was deployed to serve the needs of the Wikipedia encyclopedia in 2002. Wikipedia and other Wikimedia projects continue to define a large part of the requirement set for MediaWiki. The software is optimized to efficiently handle large projects, which can have terabytes of content and hundreds of thousands of hits per second. Because Wikipedia is one of the world's largest websites, achieving scalability through multiple layers of caching and database replication has been a major concern for developers.
The software has more than 800 configuration settings and more than 2,000 extensions available for enabling various features to be added or changed. On Wikipedia alone, more than 1000 automated and semi-automated bots and other tools have been developed to assist in editing.
It has also been deployed by some companies as an internal knowledge management system, and some educators have assigned students to use MediaWiki for collaborative group projects.