A few highlights from their website…
The Best Web Annotation Service: Add highlights and sticky notes on any web page, anywhere, and access them anywhere.
A Great Webpage Clipping Tool: Highlighted portions of any webpage are clipped and collected centrally, which can be shared and searched.
An All-in-One Bookmarking Tool: Bookmark webpages to Diigo, local folder, del.icio.us , Simpy, Furl, Spurl… and make them permanently cached and full-text searchable.
A Great Collaborative Platform: Share and interact on online findings, complete with highlights and sticky notes.
The Most Customizable Search Tool: Like Google’s toolbar, but far more customizable, so you can access any search service with one-click — music, maps, references, local library, New York Times, …
Unique Content Selection Menu: Interact with any word on a webpage just by selecting it, no click needed! - highlight, search, look up - whatever you you want!
