MindMeister is a mind mapping/brainstorming/note taking/etc web app
MindMeister is a “collaborative mind mapping” app, that could be a nice tool for classroom use.
The software supports all of the mind mapping tools that you are used to and also offers iOS and Android apps. As for pricing, there is a free plan which is limited to 3 mind maps and also paid educational plans starting at $1 a month.
Sign up is pretty easy, the website supports Google and Office 365 log ins for sign up, along with a few other choices.
