I wanted a smallish shelf that could bolt to just one side of a conventional server rack. (My use case was to provide a temporary resting place for a Le Potato that currently is running MagicMirror on my home server). This was the first prototype: I can imagine a number of additions that will make it better (most noticeably, adding a lip along the left and back edges, both to stiffen the shelf and to keep stuff from sliding off the back, but I printed one, added some velcro to hold the Le Potato in place, and it's serving some purpose in homelab. Placed here in case you find it of use. Designed with OnShape.