I had 4 Nintendo DS lites laying around and a NDS flash card.
I wanted to get them talking with a RPI and a Arduino board. I had a Wiznet W5200 shield laying around, so I decided to use that for now. A get request is used on the NDS side to talk with the Arduino server. The server has code that will parse the GET URL, for example: sending /?H6 will set GPIO 6 to high.
It works pretty well being mounted above a lutron light switch.
Currently only does:
Change GPIO states for Test LEDs, the pins not used by the shield.
Talks to another Arduino Uno that is controlling WS2812 lights on the crown molding around the perimeter of the room.
Switches on/off relays for controlling my twilight laser star projector.