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 successful project of sharing of free knowledge (one of the ten most popular websites). The project has shown to many people that free knowledge works and how the concept of collaboration adds value to our world.

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, that collect other types of free knowledge, for example:
 * Wikibooks (free text books)
 * Wikisource (free-content library)
 * Wikiversity (sharing of knowledge)
 * Commons (media repository)
 * Wiktionary (dictionary and thesaurus)