For collaborative mind maps check out Coggle at http://coggle.it.
Whether you’re taking notes, brainstorming, planning, or doing something awesomely creative, it is super simple to visualise your ideas with Coggle. Share with as many friends or colleagues as you like. Changes you make will show up instantly in their browser, wherever they are in the world. – Coggle.it
Create a free account at http://coggle.it
Create a diagram and then invite colleagues/ students to collaborate on the mind map.
Click on the central grey box and give the map a title. Use the + on the central box to branch out and add more content. Users can add text, pictures and hyperlinks.
Once completed, the mind map can be downloaded as a PDF or PNG file, for free.
Users can upgrade for $5 or $8 a month, unlocking additional features and memory.