What kind of software have you written? Open source projects you have worked on that are on github? Microcontrollers you have programmed for home automation?

What kind of software have you written? Open source projects you have worked on that are on github? Microcontrollers you have programmed for home automation? What have you done that proves to a company you can write software? A coding challenge for 1 hour is the minimum. It isn't a real system that does useful stuff. What can you show them that is real?