Many peripherals with serial interfaces still use AT commands - Bluetooth <-> Serial adapters, the original ESP2866 firmwares where it was a Wifi-to-Serial adap

Many peripherals with serial interfaces still use AT commands - Bluetooth <-> Serial adapters, the original ESP2866 firmwares where it was a Wifi-to-Serial adapter, most Serial <-> CANBus/OBD adapters like ELM327, basebands all spring to mind.