First up, personal brain. This provides for the construction of a traditional mindmap. It is very user friendly and intuitive to use. It has comprehensive features which allow you to link to your files, webpages etc. so that it becomes an extension of your usual filing / folder system on your desktop. A guide to ways to use personal brain is a good summary of the uses for mindmaps.
The other was dropmind which is available as a web version or desktop version. This is a more visually exciting platform & the web version allows multiple users to edit and share a mindmap. Presentations can also be generated. The user guide is a pdf file (compared to personal brains series of videos) but the interface is intuitive and user friendly and should not be difficult for students engage with after a short introduction.
Another interesting concept is xtimeline. This nifty site has a collection of timelines ranging from the history of tea to economics to notables like Steve Jobs and Beethoven. There is also a history of the internet which is open for public editing. You are able to make use of the timelines posted by other users as a resource or built ones yourself. Each node in the timeline is a link to more information including pictures and videos. Individuals or groups can work on each timeline so this resource is ideal for use in education.