This is the most fully featured mind-mapping software that is also free. You can use the iOS app or online version (which runs a little smoother). The free version also allows you to add images and change colors.
This was the app I used to make my lesson plans for about a year and a half. It has many of the same feature of Mindmup, but I find it to be more intuitive and elegant. The downside is that the free version is missing some key features like color selection, Dropbox integration, and the ability to add images and photos. There is also no online version and the desktop version is pricey.
Designed specifically for kids, this was by far the simplest and most intuitive of the mind-mapping apps I tried. Making the maps are a breeze and the ability to draw your own pictures is really helpful. If I needed one mindmapping tool to use with elementary-aged students, this would be it.
Text 2 Mind
Text 2 Mind is one of those ideas that you’re surprised no one ever thought of before. Instead of pointing or clicking for new cells in your mind map, you write an outline which is then converted into one. It’s surprisingly intuitive to use and, for some students, might be a better option. Some down sides are that there is no mobile app and you cannot save your progress unless you buy the paid version (though you can download your mind map as a PDF).
Holt Interactive Graphic Organizers
This site has a list of graphic organizers that can be filled in online or printed out to be completed with pencil. This isn’t going to win any awards for ingenutity, but it serves its purpose well and could be the best option for some people.