The cable is easiest way ever to connect to your microcontroller/Raspberry Pi/WiFi router serial console port. Inside the big USB plug is a USB<->Serial conversion chip and at the end of the 36" cable are four wires

The power pin provides the 5V @ 500mA direct from the USB port and the RX/TX pins are 3.3V level for interfacing with the most common 3.3V logic level chipsets.

Also handy for hacking WiFi routers to install alternate OS's, or nearly any other TTL port. This is easier to use than an FTDI cable in many cases because the wires are separated This cable is not good for Arduino re-programming such as a Boarduino, MENTA, Monochron, etc. because it does not have the DTR/RTS wire necessary for initiating the bootloader reboot sequence.