JXFire is a Multi-User Dungeon game written in Java. It is using the Sun Gaming Server (aka "Project Darkstar") framework. JXFire aims at testing various game mechanisms rarely used, like uncertainty in gaming data perception, self-organizing ecological systems, or non-instantaneous information propagation.
PodSixNet is a lightweight network layer designed to make it easy to write multiplayer games in Python. It uses Python's built in asyncore library and rencode.py (included) to asynchronously serialize network events and arbitrary data structures, and delivers them to your high level classes through simple callback methods. Each class within your game client that wants to receive network events subclasses the ConnectionListener class and then implements Network_* methods to catch specific user-defined events from the server. You don't have to wait for buffers to fill, check sockets for waiting data, etc. Just do connection.Pump() once per game loop and the library will handle everything else for you, passing off events to all classes that are listening. Sending data back to the server is just as easy by using connection.Send(mydata). Likewise on the server side, events are propagated to Network_* method callbacks and data is sent back to clients with the client.Send(mydata) method.