Google Knol, which looks like it could be a direct competitor to Wikipedia opened for users yesterday.  Knol is "authoritve" articles which emphasize authorship.  The point behind this is you know who is writing the content.  Wikipedia has fallen under criticism for users being able to manipulate articles without leaving much of a papertrail.  Knol seems to seek to avoid these kind of issues.

Another feature is called "moderated collaboration" where a user can accept, reject, or modify entries posted by other while still retaining ownership of the article.  The interface is much more streamlined than Wikipedia, and much more easier to use, especially for new users.  It will be interesting to see how this service develops over the next few months.

Link: Google Knol