Run pfSense on it as your router, using VLANs to make use of the single NIC on it. I've done this myself, and it was a great learning tool. You get the benefi

Run pfSense on it as your router, using VLANs to make use of the single NIC on it. I've done this myself, and it was a great learning tool. You get the benefit of having a built-in UPS too. Note that you'll need a switch capable of supporting VLANs too, but you can pick these up very cheaply nowadays.