1. A haptic interface system comprising: a haptic interface device movable by an operator in at least one direction of displacement, the haptic interface system providing resistance forces to the haptic interface device; a controller for receiving a variable input signal and providing a variable output signal, said controller adapted for running a program that processes said variable input signal and in response derives said variable output signal; and a magnetically-controllable device that receives said variable output signal and provides said variable resistance force in proportion to said variable output signal, said magnetically controllable device comprising a volume of a magnetically controllable medium, the variable resistance forces being provided by changing the rheology of the magnetically controllable medium in response to said output signal to thereby directly control the ease of movement of the haptic interface device, said variable resistance forces being provided to resist displacement of the haptic interface device by the operator in at least one direction of displacement of said device.