The package comes with a simple command-line tool to control relays. For example, to turn on both relays on a two relay board: ...

There was a time when if you bought a USB mouse, in the box was also an adapter ... it may well have come with an adapter for a 9-pin RS232 serial port. Those mice from a decade or more ago ...

My LG TV has an RS232 Service Port that can be used to control the TV (including Power On) via the serial protocol. I initially used a Raspberry Pi with a USB to Serial adapter and it worked great.