Here is the difference between Wikipedia Encyclopedia and the newly introduced Google Knol.
Wikipedia was founded in January 2001. It has more than 8.2 million articles in more than 200 languages, including more than 2 million in English.
Wikipedia is not ad-supported, but instead supported by the nonprofit Wikimedia Foundation.
Google Knol, is a user-generated encyclopedia, collaborative reference site.
Knol allows its authors to earn a profit from their articles with ads.