There is also WebCL, an effort underway to put OpenCL in the browser, and River Trail, an experiment to execute subset of JavaScript using OpenCL as a backend.

There is also WebCL, an effort underway to put OpenCL in the browser, and River Trail, an experiment to execute subset of JavaScript using OpenCL as a backend. I don't know how difficult it is to write a CPU compute device driver, so I don't know if WebCL will become a viable general stategy for multicore execution in a browser though.