I was tipped off by a colleague this week that Google's knowledge management play, Knol, has recently been launched.
The Knol home page clearly states that a Knol is "an authoritative article about a specific topic."
Whereas Wikipedia is a somewhat "open" environment, inviting everyone to contribute to dynamic articles, Knol mandates the creation of an article by a single user, which is unalterable. Users can comment upon the content, ask questions, and rate the value of a Knol, but they cannot edit it.
The other major difference is that Wikipedia's contributors are mostly anonymous (unless you look at the history, but even then it displays login names) and Knol requires the expert be credited and take their bows or lumps.
At Knol, I saw plenty of contributions by medical doctor's about all sorts of medical conditions (which seems to be the majority of the content at this time) and a recipe for excellent pancakes.
Hey, the site is very new and Wikipedia has a 7 year head start - if that even matters. Knol is ripe for all types of content and should be interesting to watch over the next few years.