A mind map is a very powerful tool to represent hierarchies or the links between ideas and a central concept.
I often draw a mind map for note taking during webinars or when studying a new subject.
It helps to bring the knowledge back my mind years later on a glance.
I used the open source mind mapping software Freemind for quite long time and I was a fan.
Recently I adopted Mindmaster that is cloud-based allow me to use it from any device.