My Multiplayer Games & Software Engineering assignment, the task was to demonstrate methods of handling data for games through a network. What I did was write a basic Server & Client library to send messages between each other, and I wrote a game with it.
I wrote the library (and named it GPNetwork :P) that has a server and client class for both TCP and UDP networks, the server and client in the program above uses the UDPServer and UDPClient respectively, where you can send messages between clients. One client can start a game, which opens up a game window for each client running.
The game, Knock Out, is a simple bumper car style arcade game. Each player controls a car that moves around the arena, and you much push off other players in the arena. Last one standing wins!