X3D is a data structure for 3D scenes and objects. It's an evolution of VRML, whose most common version dates back to 1997. X3D is an ISO standard. X3D files can actually be stored in three different formats, all sharing the same underlying object hierarchy: XML, Classic VRML (also a text file, close to VRML), and Binary (less common). For more informations, the reference site is web3d.org.
X3D files include not only 3D shapes, their appearance, light sources, viewpoint positions and properties; but also support for animations, interactivity and scripts.
You can experiment with this online playground, or here with Sysquake support.
Calerga VR doesn't implement yet the complete X3D specifications. Besides, it adds new fields, nodes, and syntactic features which we think are worthwhile for our target applications. Its current implementation is described on this page.
By virtual experimentation we mean the transposition of an experimentation to virtual reality, backed by accurate models and simulations, which provides a close involvement from the user (typically by touching virtual devices) to let her understand how the system under study reacts.
Here are four virtual experiments in the domain of automatic control created with Calerga VR, where Sysquake js helps to develop effective controllers: