Next, Diigo is a web highlighter and social bookmarking tool, plus much more! This link is the link to the Google Search for Diigo. It is a little easier to navigate for a first time user. Click on the “About Diigo” and a “Guided Tour” for your introduction!
http://www.google.com/search?client=safari&rls=en-us&q=diigo&ie=UTF-8&oe=UTF-8