This is called as CoreXY mechanism.
Linear motions of violet object along X and Y axes are controlled by red and orange driving pulleys.
The black timing belt is fixed to the violet object. It connects the red driving pulley with pink pulleys.
The red timing belt is fixed to the violet object. It connects the orange driving pulley with yellow pulleys.
When red and orange pulleys rotate in opposite directions at the same velocity, the object moves along X axis.
When red and orange pulleys rotate in the same direction at the same velocity, the object moves along Y axis.
When only one driving pulley rotates, the violet object moves obliquely.
The green line is trajectory of a point on the object.
The mechanism can be used for 3D printers.