WebCL 1.0 is based on the OpenCL 1.1 Embedded Profile and can be layered on any conformant OpenCL 1.1 or OpenCL 1.2 implementation. WebCL also boasts interoperability with WebGL.
Besides putting out the specification and other documentation, the Khronos Group has also made available an open-source WebCL validator and an open-source OpenCL to WebCL kernel translator.
The Khronos Group announced WebCL 1.0 today at the Game Developers' Conference. The press release with WebCL 1.0 details can be found at Khronos.org.
Khronos also announced today the OpenCL 2.0 Adopters Program.