Arianne is an engine to develop multiplayer online games like Stendhal
...The engine Marauroa provides a simple way of creating games on a portable and robust server architecture. Marauroa manages the client server communication and provides an object orientated view of the world for game developers. It handles database access in a transparent way to store player accounts, character progress and the state of the world
An Open Source portable pure Java game library with example games, Swing-based sprite animation engine, deployment framework, and firewall tunneling networking. The code is documented in the book Advanced Java Game Programming by David Wallace Croft.