Diigo is a personal research tool allowing one to keep highlighted portions and sticky note comments on web pages of personal/professional interest. The collaborative element allows users to conect with others sharing similar interests. The site also offers educator accounts that support accounts for an entire class.
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Kelvin Thompson (Faculty)
I've used Diigo with multiple courses over the past three years, and I've found it a wonderful resource for student learning! I've introduced Diigo as an optional tool for students organizing the plethora of web resources shared in one graduate class only to have several students say that Diigo was the tool that they would be continuing to use after the course is over. I've also prescribed use of Diigo for both required and extra credit "annotated web bibliography" assignments. Students are amazed by the power of leaving a course with access to 10+ unique annotated web resources from every student in class! (The ability to establish a group and delineate a "tag dictionary" as a starting point is extremely helpful!) I have not formally used the highlighting or "stickies" features with students, but these clearly have great potential as well.
Browser toolbar integration is one of Diigo's most useful features, but some browsers are better integrated than others. The developers appear to be working to keep up despite disparate code bases, though.