This looks good: I've got three HP NUCs like in TFA + three Pi on my desk (got more than that altogether) and it's indeed a cable mess.

> Aluminium extrusions are bars with a groove on all four sides. These bars have a standard format and you can slide all kinds of equipment in there and lock it in place with set screws. It seems to be used a lot for home made 3D printers, CNC machines and whatnot.

They're also called "T-slot" and 80/20 (from the brand).

https://en.wikipedia.org/wiki/T-slot_structural_framing

Plenty of free 3D models for tiny parts for those that can be printed at home (careful though: most won't hold much weight).