ATI Stream is the OpenCL library for AMD/ATI graphics cards. This uses the GPU of your graphics card to perform highly parallel computations. The code is however functional also without the right hardware and also development is possible, say, on a many years old laptop with Intel graphics - like the one this is typed on.

The AMD SDK is non-free. amd64 and i386 binaries are provided directly from upstream and can be installed tediously but easily. Some good soul named nou has prepared .debs from that binary distribution [1]. It is suggested to also install the non-free ATIProprietary [2] drivers to experience the true performance.