Knol

Knol is a discontinued Google project and service in favor to be replaced by Annotum. It was closed on April 30, 2012, and all content was deleted by October 1, 2012. The project's purpose was 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 it's beta phase July 23, 2008, with a few hundred articles mostly related to health and medical topics. 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 users could post comments below an article to discuss about the subject.

Google defined the lower case knol as a "unit of knowledge", which is referring to an article in the project. Several experts saw Knol as Google's attempt to compete with Wikipedia as others pointed out the differences between them.

On January 16, 2009, Google announced that Knol had grown to over 100,000 articles, and users from 197 countries visited Knol on average. Since then, the Public Library of Science Currents Influenz and the Harvard University-sponsored forum for Healthcare Information Technology (HIT) Platform have utilized Knol-based collections for rapid exchange of research.

On the website, they've given a final message about it's stopping point.

Knol has been discontinued as of May 1, 2012

''Knol has been discontinued as a service, but we've worked with Solvitor and Crowd Favorite to create Annotum, an open-source platform based upon WordPress that allows you to continue authoring and publishing scholarly articles. To learn more about this announcement, see our Frequently Asked Questions.''