This project is an Arduino based network status monitor. Eric Ayars wanted a unit to serve as an early-warning system for network problems so he concluded using LED as signs. When the leds light green the system is fine, when the leds light red Arduino is detecting a problem and when the leds light yellow-orange the Arduino is unable to detect the system status. The unit is able to monitor 13 systems and the software requires two separate programs: one to run on the host machine and determine the status of the various machines on the network, one to run on the Arduino and control the lights based on the information it gets from the host. Check details on the link below.
Arduino Network-status indicator - [Link]