HyperPhysics - Concept maps and definitions
"HyperPhysics is an exploration environment for concepts in physics which employs concept maps and other linking strategies to facilitate smooth navigation. For the most part, it is laid out in small segments or "cards". The entire environment is interconnected with thousands of links, reminiscent of a neural network.
The side bar contains a link to the extensive Index, which itself is composed of active links. That sidebar also contains links to relevant concept maps."