Castle Game Engine is using X3D as our scene graph. This means that we have a huge number of nodes (like
IndexedFaceSet) that are nicely documented in the X3D standard. And you use these nodes throughout the engine (by loading files, like X3D files, or constructing the scene using these nodes from Pascal code — see example here or (2D) here).
As our engine grows, and we get more features, I also propose some extensions to X3D, to add more features both to X3D and to Castle Game Engine. I decided to summarize them in the wiki:
Some of these proposals are already implemented in Castle Game Engine (e.g. CommonSurfaceShader, consistent RGB texture treatment, shadows). Some are planned (e.g. PBR, and binary meshes using glTF integration). All the comments are always welcome!
We also talk about these things on x3d-public mailing list, and I encourage everyone to join. If you have an opinion how X3D should look like (in the context of Castle Game Engine usage, or not!), or if you wonder how to do something using X3D — this is the list