OSX includes terminal emulation software that you can use from the command line, so we only need to install the USB drivers for the cable.
Next, install the latest drivers for the cable chipset.
There's two possible chipsets. The older cables use Prolific brand, the newer cables (as of 2017) use SiLabs brand. If you're not sure which you have, just install both drivers! There's no risk and the cable will work no matter what
For the "Prolific Chipset" cable, grab the drivers from here
(If using Lion or Mountain Lion or later OS X, you can also try this driver here http://changux.co/osx-installer-to-pl2303-serial-usb-on-osx-lion but try the official one first!)
And if you're using an older version of Mac OS X (10.8-10.6) then try this Prolific driver version 1.5.1.