This video, via CZRider01, is a demo of a DIY R.A. Moog 959 X-Y Controller clone.

Here’s what he has to say about it:

I kept the construction as close as possible to the original 959. The 959 X-Y controller has a rocker switch on each axis for either full or 10% voltage swing. In the 10% mode, pitchbending is about two semitones up or down. The demo is patched into a 1969 R.A.Moog IP system. The 959 is powered from a +10/-10 volt supply from a Minimoog. This 959 clone has an added red S-trigger button so it can be used with a keybioard or as a stand alone controller.

The 959 was offered as a modular accessory in the late 60’s, and also offered as a Minimoog asccessory in the early 70’s.