Digital technologies and online crowdsourcing allowed encyclopedias to break away from traditional limitations in both breadth and depth of topics covered. Wikipedia, a crowd-sourced, multilingual, open licence, free online encyclopedia supported by the non-profit Wikimedia Foundation and open source MediaWiki software opened in 2001. Unlike commercial online encyclopedias such as "Encyclopædia Britannica" Online, which are written by experts, Wikipedia is collaboratively created and maintained by volunteer editors, organized by collaboratively agreed guidelines and user-roles. Most contributors use pseudonyms and stay anonymous. Content is therefore reviewed, checked, kept or removed based on its own intrinsic value and external sources supporting it.