Xj3D is an open source X3D browser, developer library and test environment for the X3D real time 3D content and delivery standard.

Xj3D is a project of the Web3D
Consortium Source Working Group focused on
creating a toolkit for VRML97 and X3D content
written completely in Java. It serves a dual
purpose of being an experimental codebase for
trying out new areas of the X3D specification
and as a library that we encourage application
developers to use within their own application
to support X3D technology.

More information on the website:
Xj3D website