From the Wikipedia link:
Boeing X-45C US UAV Experimental 2002 Prototype Tailless
Boeing X-48 US UAV Experimental 2007 Prototype Tailless
Lockheed A-12 US Jet Reconnaissance 1962 production
Lockheed SR-71 Blackbird US Jet Reconnaissance 1964 production
I don't find any examples of a RC Borg cube, but if one wanted to make [one], one might start with Alexander Graham Bell's tetrahedral kite.
https://i.imgur.com/yztNlIP.jpg
If you want to give it a try, ask me about
adaptive subdivision.
edit: Okay you don't have to ask.
A tetrahedron inscribed in a cube:
Based on Bell's kites it would fly oriented with a vertex up. The inner tetrahedron could be a Rogallo Wing. With some propulsion.
Then it would be encased in a layer at the scale of Bell's kite, with an outer layer fine enough that you can paint greebling on it. Bell couldn-t be bothered with the fine scale because he didn't have CNC routers and 3D printers.
With
Auxetic materials one could make the flying head from Zardos.