They scanned a bunch of books, and then allowed search results to hit them. They then only show a small context around the hit to avoid copyright infringement.
Bibliography:
When they disabled this from Chromium, it was one of the things that prompted Ciro Santilli to switch to Proton Pass.
Very similar to OurBigBook.com!
Video 1. How to use Google Knol by Hack Learning (2011) Source. One of the last users of the website for sure! The owner of that YouTube channel is a Mark Barnes:
Video 2. Jimmy Wales on Google's Knol (2008) Source.
Replying to a listener phone-in question WNYC radio, mediated by Brian Lehrer. It was about to launch it seems, and it was not clear at the time that anyone could write content, as opposed to only selected people.
Jimmy then corrects that misinformation. He then clearly states that since there can be multiple versions of each article, including opinion pieces, like OurBigBook.com, Knol would be very different to Wikipedia, more like blogging than encyclopedia.
Video 3. Google Knol: the future of academic journals? by Doug Belshaw (2010) Source.