百度百科
The English Wikipedia, which was started in 2001, became the world's largest encyclopedia in 2004 at the 300,000 article stage. By late 2005, Wikipedia had produced over two million articles in more than 80 languages with content licensed under the copyleft GNU Free Documentation License. As of August 2009, Wikipedia had over 3 million articles in English and well over 10 million combined in over 250 languages. Wikipedia currently has articles in English. Since 2003, other free encyclopedias like the Chinese-language Baidu Baike and Hudong, as well as English language encyclopedias like Citizendium and Knol have appeared. Knol has been discontinued.