A system for controlling operation of a computer. The system includes, a sensing apparatus configured to obtain positional data of a sensed object controllable by a first user, such positional data varying in response to movement of the sensed object, and engine software operatively coupled with the sensing apparatus and configured to produce control commands based on the positional data, the control commands being operable to control, in a multi-user software application executable on the computer, presentation of a virtual representation of the sensed object in a virtual environment shared by the first user and a second user, the virtual representation of the sensed object being perceivable by the second user in a rendered scene of the virtual environment, where the engine software is configured so that the movement of the sensed object produces control commands which cause corresponding scaled movement of the virtual representation of the sensed object in the rendered scene that is perceivable by the second user.