Today I got a message from my students (who have a midterm with me tomorrow) that they were implementing one of my tools to help them collaboratively study!
This mindmapping tool is relatively easy to use and has an interface that looks like MS Office.
There are collaborative capabilities and the ability for multiple users to make changes and comments.
WHat I like is that you can export your mindmap into various formats.
FOr example, when exporting to Word, it gives you a document outline with all your topics and subtopics as different levels of headings, so you can just plug in the text.