Wanted to test a Microchip ENC28J60 ethernet controller chip. That chip is 3.3V and 5 V tolerant. So decided to test on the PC par port first. Ended up writing a complete UDP ARP subsystem in C, this will add ethernet for next to nothing to anything that has an 8 bits port.
formatting link
Those who know netcat will see I wrote a netcat clone on top of the UDP layer.
Version 0.3 is on the site, it has default gateway and netmask option added, so it can work worldwide via a router. Would you believe that was only 10 lines of extra code?