The SEL 3555 on the high end of the RTAC family. It’s an RTU supporting Modbus, DNP3, IEC 61950, and GOOSE protocols. It’s most commonly used as a data concentrator for large point counts. It’s now being used to do control of several solar power plants, replacing an industrial PLC. It has fairly basic HMI capabilities built-in, though not like what you can do with most commercial HMI applications.