This is a quick explanation on how to use the repeater program. It will need a lot of extra work, but I know people are looking for this, so I'll put it up. If someone would like to familiarize themselves with it more and make this page nicer and more complete, I would be very appreciative.
First, start the repeater program (Make sure D-RATS is not open so the serial port is free). If you're on Windows, run repeater.exe. On Linux or MacOS, run ./repeater or ./repeater.py. This will open the repeater window that looks like this:
If you want to use it as a repeater with multiple radios, add both of your serial ports in the top portion. If you want to accept network connections as well, leave the appropriate box checked. Type in an identification string and then hit the "On" button. It will start repeating.
If you want to use it as a network proxy (instead of or in addition to the repeater function), you'll need to configure D-RATS to use the network port instead of the serial port. Go into the Main Settings box, under the data tab. Where you would normally put in your serial device, put in a string as shown here:
The format is: net:IPADDRESS:PORT
Hit "Save" and you should see a message in the main window indicating that it's connected to a network port. Be sure that the remote machine doesn't have a firewall, or if it does, that the appropriate port is opened.