MiniCL includes a cross-platform run-time frontend based on pthreads, Win32 Threads, or libspe2 for Cell SPU.
It is there, to bridge the gap until OpenCL is more widely available.
See Bullet/Demos/VectorAdd, influenced by NVidia OpenCL Jumpstart Guide:
http://developer.download.nvidia.com/OpenCL/NVIDIA_OpenCL_JumpStart_Guide.pdf
