A web app by Julian Garnier for building and manipulating 3D shape creations in CSS. The interface is genius. One panel shows you the creation from an angle so you can see the 3D-ness of it and spin it around. The other three panes show you the creation from different straight on angles so you can drag them around in the relevant directions.
Check out a demo if you aren't impressed yet.
In the Preview Mode there is a button where you can one-click move it over to CodePen. How 'bout that?