Google today introduced Knol, a Wikipedia style encyclopedia that anyone can edit but with some major differences:
a) Wikipedia has one page per topic but that limit is relaxed on Google Knol – multiple authors can write on the same topic at different places.
b) Wikipedia is currently free of advertising but contributors at Know do get an opportunity to monetize content that they share on Knol through Google AdSense.
c) All content on Wikipedia is available under "GNU Free Documentation License" but Google Knol users can pick any of the Creative Commons licenses for their articles.
d) On Wikipedia, you cannot create pages for self-promotion while that’s not the case with Knol as their content policy clearly says – "You may use Knol to create articles for your business or to promote your lawful products or services."
e) Anyone can edit (most) pages on Wikipedia but with Knol you have an option to invite only selected reviewers / experts to change pages that you have created. This prevents vandalism though the scope is limited only to experts whom you know.
f) Anyone can rate articles on Knol or even leave comments just like a blog. That’s missing in Wikipedia.