Open Source Virtual World and MMOG Development Platform
3D Client (Windows), Server, and Tools to easily create massively multiplayer games and virtual worlds.
If you want to contribute to the source code please go to https://github.com/multiversemmo/MultiversePlatform
An alternative/custom Minecraft server, written in Java, compatible with the original protocol. OpenCraft is built upon Apache MINA, SLF4J, Jython and XStream. The aim is to have features not in the official server distribution, like antigrief/scripting.
A graphical isometric multiplayer virtual reality server in MUD-style. Rooms and server code can be changed online. At the moment, there is also an IRC link. Clients are available in Java and Python/C.