Metro is a library for Arduino (arduino.cc).
It facilitates the implementation of recurring timed events like:
* blinking LEDs
* servo motor control
* Serial communication
Project #2: Extend the timer-based traffic lights project to include two 'crossing indactors' for pedestrians, and a crossing button to initiate a crossing.
A simple Arduino project: making a timer-based traffic light controller, complete with sample sketch and schematic. All you need is an Arduino, a breadboard, some jump leads and three LEDs.