An arm to hold the cables for a rack mounted server (when combined with a few feet of threaded rod). The end result lets you work on a server while its fully extended from the rack without having to unplug everything. Something like this one from APC.

Everything is parameterized near the top of the OpenSCAD file so it should be pretty easy to adapt this if your dimensions are a bit different. The one number you're most likely to have to change is `computer_barrel_z`, the height of your computer mounting compared to the cable management arm. If you're using a 4U case like me my value might work. If you don't have space for vertical PCI cards then you'll need to tweak the mount.