Mind maps and concept maps are diagrams graphically showing relationships between ideas or other pieces of information. Mind maps and concept maps are related but not identical. "A Mind map reflects what you think about a single topic, which can focus group brainstorming. A Concept map can be a map, a system view, of a real (abstract) system or set of concepts. Concept maps are more free form, as multiple hubs and clusters can be created, unlike mindmaps which fix on a single conceptual center." (attribution)
Free Mind Mapping Software
Bubbl.us (Web 2.0; no client download required)
Compendium (has some attributes of Concept Mapping)
XMIND (maps can be exported to Word and PowerPoint)
FreeMind
Free Concept Mapping Software
Cmap
