Diigo is an awesome tool to use in the classroom. Teachers across the globe have used the social bookmarking tool to motivate and engage students in collaborative learning
such as displaying an excerpt from a work on a smartboard as long as the work is not commercially available for purchase.
The use of works that are legally available from a freely accessible website is also allowed as long as there is no clearly visible notice prohibiting the use of the work or there is no technological measure limiting access to the work.