Hello Community Member!
Recently I needed a Software for a really sophisticated Project.
In order to keep my thought together and to communicate them right to my customer I did a search on the web for a mindMapping tool.
This one is fantastic cross-plattform and is released under GNU GPL.
http://www.xmind.net/
It's very userfriendly, featurerich and intuitive.
You can create MindMaps and Organisational Structures as well. And more you can do.
Enjoy!
Regards,
Stefek