Virtual reality 
VRML is by now the most diffused standard language for 3D world models on the Web,

X3D is an open standard for 3D content delivery. It is the next revision of VRML. X3D files can be displayed with a X3D plugin, program, or toolkit. Most of the X3D plugins also display VRML files. X3D has been approved as an ISO International Standard. VRML models can be converted to X3D with the VRML to X3D translator.

For cross-platform developments, have a look at and by the Fraunhofer Institute A new evolution of standards is coming, together with the HTML5 wave..

An old small world model archive here