A Knol is a unit of knowledge, well according to Google that is. Their new information source has been moved into public Beta. Basically Knol is sort of like Wikipedia but each entry is authored by a single individual who has complete editorial control. Google provides the following outline in the help:
So what subjects can I write on?
(Almost) anything you like. You pick the subject and write it the way you see fit. We don’t edit knols nor do we try to enforce any particular viewpoint – your knol should be written as you want it to be written. Of course, Knols are subject to Terms of Service and Content Policy to ensure a good experience for all users and compliance with applicable laws.
What if someone else has already written an article on that subject?
No problem, you can still write your own article. In fact, the Knol project is a forum for encouraging individual voices and perspectives on topics. As mentioned, no one else can edit your knol (unless you permit it) or mandate how you write about a topic. If you do a search on a topic, you may very well see more than one knol in the search results. Of course, people are free to disagree with you, to write their own knols, to post comments and ratings.
Can I collaborate with other authors?
Of course. For each knol you can choose to write on your own or collaborate with other authors.
An interesting experiment, as mentioned by Mashable is might just end up like Squidoo but it could also turn into something completely different. I could also see the format working internally to organisations for building content. Some organisationa have not yet got their minds around wiki’s allows anyone to edit, where a tool like Knol might be used as a stepping stone towards wikis.