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I use Fusion 360. It is a little bit of an overkill for relatively simple designs as these (simple extrusions), but it is the CAD software I am more familiar with. I use a picture (that i found in http://stevencrewniverse.tumblr.com/ a long time ago) as a canvas, and then make a sketch over it. Finally, I extrude sections with different heights in order to give depth to the design (I guess it could be considered a 2.5D design).
It is actually very simple, just a little time consuming. The difficult part is the rendering (also done in Fusion 360) since it is difficult to get the correct light and angle in order to show the relief properly.
When I have all diamonds I am planning something special. I hope someone can print (or mill) one of these designs.