Google has now launched its Wikipedia rival, Knol, making the beta site available to everyone.

Similar to the infamous online encyclopedia, "knols" are authoritative articles about specific topics, written by people who know about those subjects.

With the aim to encourage these people contribute their knowledge online and make it accessible to everyone, it differs from Wikipedia in that there's more emphasis on who writes each knol.

Google says the key principle behind Knol is authorship: "Every knol will have an author (or group of authors) who put their name behind their content. It's their knol, their voice, their opinion. We expect that there will be multiple knols on the same subject, and we think that is good".

Rather than a free-for-all editing sytem, Knol works with "moderated collaboration". This means a reader can make suggested edits to a knol which the author may then choose to accept, reject, or modify before these contributions become visible to the public.

Also different from Wikipedia is that authors can profit from their articles. Writers can chose to include ads from Google's AdSense program. If an author chooses to include ads, Google will provide the author with a revenue share from the proceeds of those ad placements.