The 2.1 version of Xj3D for Mac was available to download on the developer's website when we last checked. We cannot confirm if there is a free download of this app available.
Please check the Mac app with an antivirus before launch as it is downloaded from the developer's website, and we cannot ensure that it is safe. The program lies within Design & Photo Tools, more precisely 3D Modeling. The actual developer of this free software for Mac is Web3D Consortium.
From the developer:
Xj3D is an open source (LGPL) 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.
You may want to check out more Mac applications, such as Microspot Interiors Pro, eBPMN or Opera SVG Viewer, which might be similar to Xj3D.