Knol was a Google project that aimed to include user-written articles on a range of topics
. The project was led by Udi Manber of Google, announced December 13, 2007, and was opened in beta to the public on July 23, 2008 with a few hundred articles mostly in the health and medical field. Some Knol pages were opinion papers of one or more authors, and others described products for sale. Some articles were how-to articles or explained product use. Other people could post comments below an article, such as to refute opinions or reject product claims.
In November 2011 Google announced that Knol would be phased out. Content could be exported by owners to the WordPress-based Annotum. Knol was closed on April 30, 2012, and all content was deleted by October 1, 2012. Between these dates the content was not viewable, but was downloadable and exportable