This applet is 4D version of building block play, that all of you played at child. At start only 1 block exist. If mousedown in left view window, all view will rotate. If mousedown on block , block will move to 3D direction.
If moudedown on small circle at right tool view window, block will rotate in 6 mode. At left 3 view, rotate in 3D axis, at right 3 view, rotate in 4D axis.
To add new block, move new block near to old block. If new one is side of old one, it will adhere to old one. Even if move old one near to new one , it will not adhere.