Knol is a Google project which aims to include user-written articles on various topics. After its first alpha phase in December last year is now available to everyone.
A knol is an authoritative article about a specific topic.
Knol: a unit of knowledge
Share Your Expertise in Google's Knol
Google Knol Is Live
Knol: Google Takes on Wikipedia - ReadWriteWeb
Google Decides to Make its Knol Site a Moderated Wikipedia
Google's Knol Launches: Like Wikipedia, With Moderation
Google Knol is now Open to Everyone
Knol - Wikipedia, the free encyclopedia