I'm generally less interested in browser-hosted applications for 3D stuff (compared to desktop apps) but this is written with an interesting combination of technologies that span desktop and web. For example, OpenCASCADE, the same library used in FreeCAD, is emscripten-compiled to run in javascript. There's a number of support libraries that make web development look much more like application development (window management, etc), controller/gui library.

It's a view of how the web could have evolved (to be a sort of transparent desktop-like application support) earlier, with greater standardization on application-style GUIs.