This is a collection of three programs written by Larry Abbot at Brandeis University which let you play with simple models of channels, voltage or current clamped neurons, and propagating action potentials. You can stimulate or not, change the stimulus duration and intensity, ionic concentrations, and a couple other things. The output is plots of current over time. You give the neuron a voltage step or current pulse and watch what happens. You can also add in a synapse though I did not quite understand what this was simulating.
Cable simulates an axon propogating a series of action potentials, using the cable equations.
Again, you can change several parameters such as the stimulus, the cable dimensions, the currents involved, and more. All of these programs are very simple compared to others in the same genre, with very little in the way of user interface. Each one has windows on the screen which show the graphs, and another window with with a few dialog boxes that let you change all the parameters. Other than that you have to figure everything out on your own. The trio of programs would make a very decent collection to be used in an introductory neurobiology course as illustrations of the phenomena students are hearing about in the lectures and textbook.