I ran into one about 10 years ago. It was a bespoke diagnostic tool for some industrial machinery. It was only needed for last resort situations to get in via serial and gracefully rescue the HMI from a freeze or sync issue where the machine found itself in an impossible state doing maintenance to prevent having to do a physical lockout and shutdown situation or something like that. Never saw it actually used though as the beast was built before laptops and USB serial adapters were a thing. It was probably collecting dust for a decade before I came across it.