Official Google Blog: Encouraging people to contribute knowledge - Google has announced that they have started inviting a selected group of people to try their new, free tool "knol", which stands for a unit of knowledge.
.."Knols will include strong community tools. People will be able to submit comments, questions, edits, additional content, and so on. Anyone will be able to rate a knol or write a review of it. Knols will also include references and links to additional information. At the discretion of the author, a knol may include ads. If an author chooses to include ads, Google will provide the author with substantial revenue share from the proceeds of those ads"..