Three small starter samples of the same translucent tetrahedron: Babylon.js, Three.js, and X3D. This is just a visual/technical comparison starter, not a game build.
Game-engine feel, practical for browser gameplay.
Flexible and lightweight, with broad ecosystem support.
Standards-oriented scene description approach.
If you use these from a local folder, you may prefer serving the folder through a tiny local web server rather than opening directly with file:// URLs.