In the early days of Socialcast, I built what I called the "pinging wall" which was a bunch of RGB leds inside of ping pong balls and mounted on the wall, each employee had their own ball. Using the arduino ethernet shield, the arduino would poll our internal deployment of our own software, basically an internal company newstream and the pinging wall would indicate whether varying levels of red, yellow and green to indicate whether you had messages or @mentions and be green when you were active on the activity stream.
next steps: use an arduino nano with an HC-06 bluetooth dongle to remove that cable. Also, another step might be using an ESP8266 and make a webserver out of it (maybe some links to get you started here: http://embeddednodejs.com/chapters.html )
