Pretty amazing what browsers can do these days. Here is Path Tracing Renderer written in JavaScript with Three.js and GLSL shaders (something I am somewhat familliar with)
https://github.com/erichlof/THREE.js-PathTracing-RendererBe sure to check out the live demos at the top of the page. I'm not sure why the ocean demo is locked at 1 sample. Maybe demonstrating real-time path tracing.
Kinda makes me want to make Terragen Project viewer. Take a gathered project, and upload it somewhere, and use a "Terragen Viewer" app online to view a project in ray or path tracing. The shader settings in the TG XML files all relate to the same stuff Three.JS is built atop, though some aspects of Three.JS are more modern/complex. Almost needlessly so, like their rotation matrixes and making it a pain to get basic euler in 0-360 degrees lol.