This simple shelf is easy to mount and is fairly strong. It prints without support with the top facing down and comes in two sizes, “square” 120mm x128mm and rectangle 180mm x 90mm. It should be easy to remix for custom applications. 

I designed it for my bathroom but could be used anywhere that you can use nails/scews.

The shelf is easily installed with 2 fasteners that the shelf slots onto. Fastener should be spaced 90mm apart for the square shelf or 150mm for the rectangular shelf.