Developing products for startups and SMEs using too many hardware and software technologies to list fully here but including:
Schematic capture, PCB layout and firmware development.
ARM, 8051, x86, PIC, ESP8266 and ESP32 processors. Interfacing using TCP/IP, Bluetooth, RS485, RS232, USB, LoRa, ADC, DAC, SPI, I2C, JTAG and many other different sensors.
Programming languages including assembly, C, C++, Python, Lua and Scheme. Compilers including GCC, Keil, IAR and LLVM.