Wikipedia

Wikipedia is a wiki project for the creation of a free-content encyclopedia. It has grown to the biggest and arguably best (human made) encyclopedia of all times and is probably the most prominent and successfull project of sharing of free knowledge (one of the ten most popular websites).

It is available in many languages and has already millions of articles in the biggest, the english language version.

There are several sister projects hosted by the umbrella organization, the Wikimedia Foundation, for example:
 * Wikibooks (free text books)
 * Wikisource (free-content library)
 * Wikiversity (sharing of knowledge)
 * Commons (media repository)
 * Wiktionary (dictionary and thesaurus)