First of all code is pure GML, so GML knowledge required to use, but can be run any OS. (tested on Windows, HTML5 and Android).
PickerJoint is special kind of joints, give very simple solution to pick and drag dynamic objects in physics world.
The effect very spectacular, weight-depend expansion, like to rubber band.
Example code short and simple, already set up all important things for active physics world.
It is maybe good start for you to make superb physics based games !
Preview : YOUTUBE