This motion platform has three motors arranged in a triangular shape to control the tilt and movement of the platform. You can hold the hub in your hand and tilt it to control the tilt of the platform using the hub's gyro sensor.
The motion frame is triangular, but you can add the optional oval platform on top to make it easy to add more items, such as the Ball Challenge, where you control the roll of a ball on the platform.
With three motors, this platform technically has three "degrees of freedom", which means that you can control three different kinds of motion. With the gyro input, you can control the pitch and roll angles of the platform, which leaves one more degree of freedom. This turns out to be the overall height (z) of the platform, which the program also lets you adjust using the hub's left and right arrow buttons.
With more motors, such as the six motors or actuators in a Stewart Platform, you could control all six degrees of freedom of a moving object (roll, pitch, yaw, x, y, z), so this is like a simplified version of that.