CmapTools is a free program used by colleges around the world for creating concept maps: graphical tools for organizing and representing our knowledge about a particular issue or system. In CmapTools, concepts (boxes or nouns) are linked together by propositions (lines or verbs) to form a network that visually demonstrates connections between issue components. By creating a visual map of what we know, one can open up new ways of understanding how that system functions and how its components interrelate; this is what distinguishes CmapTools from more traditional (e.g., verbal) modes of thinking and communication.
also check http://cmapskm.ihmc.us/servlet/