Alper Yazar has posted an update on his open source isoUSBRS422 project.
As I said, basically it is an USB ↔ RS-422/RS-485 converter board. It can be used to communicate devices with RS-422/RS-485 interface by using a USB port of PC. Also, ground of USB port is isolated from ground of RS-422/RS-485 channel. It may help you to prevent ground loops in large systems. If you are not sure whether you need isolation or not, probably you do not need it.
More info at Alper’s project page.
You can find the tutorial videos here.