I wanted a second little shelf in my sink.  Couldn't find one, so made it.  Making it mate up in a stable way was a bit annoying (maybe I should have started with the calipers or a paper mock ) but it's sufficiently stable for my use-case so I figured I'd share..

I avoided any creative flourishes because I could only picture them picking up filth (even drainage slots).  However, I used a textured plate because that seems likely water-proof but higher friction than a smooth plate.