org-brain implements a variant of concept mapping in Emacs, using org-mode. It is heavily inspired by a piece of software called The Brain, and you can view an introduction to that program here. They also provide a blog with great ideas of how you can think when organizing your Brain. You can think of org-brain as a combination of a wiki and a mind map, where each wiki page / mind map node is an org-mode file which resides in your org-brain-path, or a headline with an ID property in one of those files. These are called entries. Entries can be linked together, and you can then view the network of links as a mind map, using M-x org-brain-visualize.