I've recently looked at Coggle for mindmapping. To me it could be a little difficult for my middle schoolers, but if it is used on our smartboard and done as a class, I think they might get the jive of it.
I agree that Coggle could be a bit too advanced for younger students. It seemed like a good choice for high school students in 11 and 12 grades and college students as well. It is a lot like Mindmeister in that you can do a lot with it, but it does have a bit of a learning curve.