Diigo, a combination Web research tool and social network. Like del.icio.us, Diigo provides a browser plug-in that lets you tag interesting information you encounter during your Web travels. But whereas del.icio.us begins and ends with social bookmarking, Diigo offers features useful for research.
You may highlight, annotate and bookmark information you find in a Web page. You may tag the information, as well as organize and share it. You may even produce a slideshow from the capture information.
Diigo further takes social bookmarking to the next level with community features that give members the ability to communicate with individuals or groups with similar interests.