Debate Graph: http://debategraph.org
18 Mindmapping Tools: http://www.educatorstechnology.com/2012/06/18-free-mind-mapping-tools-for-teachers.html?m=1
Popplet: http://popplet.com/app/#/home
Bubbl.us: https://bubbl.us/
Mind42: http://mind42.com/
MindMeister: http://www.mindmeister.com
Mindomo: http://www.mindomo.com
Coggle.it: https://coggle.it