Concept Mapping

Concept mapping (aka mind mapping) is:

A tool for assisting and enhancing many of the types of thinking and learning that are required at university
A graphical way of organizing thoughts and showing how concepts are related or differentiated.
Connections are labeled by cause/effect, relationships, and inter-relationships, differences, or hierarchies.

There are several apps that use concept mapping:

Mindmup2- web-based app that can be saved using Google Drive

Simplemind - app for iOS systems

ExamTime - web-based app