As part of the Northern Ireland Raspberry Jams, we have access to a old full sized traffic light that was found while in the process of getting scrapped.
The activity in this section makes use of this traffic light and David Whale's excellent network.py library, a massively simplified networking library for Python.
Note, this must be installs on all the Raspberry Pis for this activity.
Some example server code is included. It works for any resources you have to share, not just a traffic light. It writes the received string to a text file which another other application can read from.