Update: For a newer neural net simulator optimized for image processing, see http://neural2d.net.
Update: For a beginner's introduction to the concepts and abstractions needed to understand how neural nets learn and work, and for tips for preparing training data for your neural net, see the new companion video "The Care and Training of Your Backpropagation Neural Net" at vimeo.com/technotes/neural-net-care-and-training .
Neural nets are fun to play with. Join me as we design and code a classic back-propagation neural net in C++, with adjustable gradient descent learning and adjustable momentum. Then train your net to do amazing and wonderful things. More at the blog: http://www.millermattson.com/dave/