He automated some Rexroth production with it.

https://www.stritzinger.com

I've wondered about something related and the origin of Erlang in the 80s/90s. Back then when it was running on the telephone switches etc, was it running bare metal? Or did those switches run an OS like some form of Unix or something else?

Not to downplay it or anything, but it is "just" the normal Erlang BEAM VM compiled together with the real time OS RTEMS (which basically implements all POSIX things that the VM needs). Of course, getting it to work needed a lot of research and and experimentation, but the end result is surprisingly simple for what it is. The maniac/genius part is coming up with the idea in the first place and actually pushing through until it works, not many people have the stamina and focus for that.

Source: I was part of the original core team, and I developed the first version of the Erlang support library and runtime.