Following eight months of testing, Google's Wikipedia competitor, Knol, was finally opened to the public today. The concept is quite similar to that used by Wikipedia, whereby users can share knowledge in a wiki format, but with a twist that emphasizes authorship and control over an article's content.

Each article - otherwise known as knol - is created by an author or team of authors who receive attribution and are allowed to insert AdSense ads on their pages to receive a share of the revenue. Any reader may suggest changes to a knol, but edits will pass through a moderation process before being applied. Readers can also rate, write reviews of, and submit comments to any given knol.

Any topic can have several articles written on it, but only the 'best' ones will in theory rise to the top while the rest fade away. By offering a monetary incentive Google hopes to lure experts on any given subject into creating good (and hopefully credible) content for the site, and a quick glance at some of the topics featured on the site already show many articles written by doctors that have to do with medical conditions. Seeing that articles will contain advertising, though, one has to wonder what is to keep Knol from becoming just another spam repository.