OpenSimulator is a 3D Application Server. It can be used to create a virtual world which can be accessed through a variety of clients, on multiple protocols. OpenSimulator allows you to develop your world using the technologies you feel work best - we've designed the software to be easily extendable through loadable modules to build completely custom environments. OpenSimulator is released under a BSD License, making it both open source, and commercially friendly to embed in products.
Project Wonderland is a 100% Java and open source toolkit for creating collaborative 3D virtual worlds. Within those worlds, users can communicate with high-fidelity, immersive audio, share live desktop applications and documents and conduct real business. Wonderland is completely extensible; developers and graphic artists can extend its functionality to create entire new worlds and new features in existing worlds.
Quest Atlantis (QA) is an international learning and teaching project that uses a 3D multi-user environment to immerse children, ages 9-15, in educational tasks. QA combines strategies used in the commercial gaming environment with lessons from educational research on learning and motivation. Participation in this game is designed to enhance the lives of children while helping them grow into knowledgeable, responsible, and empathetic adults.