 Several attempts have been made to create a multi-user three-dimensional environment or 3D GUI, including Sun's Project Looking Glass, Metisse, which was similar to Project Looking Glass, BumpTop, where users can manipulate documents and windows with realistic movement and physics as if they were physical documents, and the Croquet Project, which moved to the Open Cobalt effort.The zooming user interface (ZUI) is a related technology that promises to deliver the representation benefits of 3D environments without their usability drawbacks of orientation problems and hidden objects.It is a logical advance on the GUI, blending some three-dimensional movement with two-dimensional or "2.5D" vector objects.