QCircuit

QCircuit is an aid for understanding, designing, and simulating quantum circuits. You essentially drag-and-drop gates into place on a set of "wires" and see its effects. Currently implements the Hadamard and Not/CNot/Toffoli/etc. gates, as well as allowing you to define a gate with an arbitrary (2^n)x(2^n) complex matrix. You can feed input bits in one end of a circuit and watch the values change as they continue through the circuit, as well as retrieving the actual quantum state at any given point. I still have a number of features I want to implement, so I will likely be updating this in the future.

If you don't want to read the help file first, just note that holding control is frequently used to group actions.

Also, the zip has a folder, "generated," which has a number of sample files generated by the program. Read the help for info on the extensions.