The Khronos Group has just ratified the standard for WebCL 1.0. The API is expected to provide a massive performance boost to web applications which are dominated by expensive functions which can be offloaded to parallel processors, such as GPUs and multi-core CPUs. Its definition also allows WebCL to communicate and share buffers between it and WebGL with an extension.
Frequent readers of the site might remember that I have a particular interest in WebCL. Based on OpenCL, it allows web apps to obtain a list of every available compute device and target it for workloads. I have personally executed tasks on an NVIDIA GeForce 670 discrete GPU and other jobs on my Intel HD 4000 iGPU, at the same time, using the WebCL prototype from Tomi Aarnio of Nokia Research. The same is true for users with multiple discrete GPUs installed in their system (even if they are not compatible with Crossfire, SLi, or are from different vendors altogether). This could be very useful for physics, AI, lighting, and other game middleware packages.
Still, browser adoption might be rocky for quite some time. Google, Mozilla, and Opera Software were each involved in the working draft. This leaves both Apple and Microsoft notably absent. Even then, I am not sure how much interest exists within Google, Mozilla, and Opera to take it from a specification to a working feature in their browsers. Some individuals have expressed more faith in WebGL compute shaders than WebCL.
Of course, that can change with just a single "killer app", library, or middleware.
I do expect some resistance from the platform holders, however. Even Google has been pushing back on OpenCL support in Android, in favor of their "Renderscript" abstraction. The performance of a graphics processor is also significant leverage for a native app. There is little, otherwise, that cannot be accomplished with Web standards except a web browser itself (and there is even some non-serious projects for that). If Microsoft can support WebGL, however, there is always hope.
The specification is available at the Khronos website.