cuBLAS-XT is the multi-gpu version of the popular cuBLAS library. There is a premier version which further extends its multi-gpu capabilities and a eval version of that is now available to CUDA Registered Developers.
Learn more about this at: https://developer.nvidia.com/cublasxt
Premier version is at : https://developer.nvidia.com/rdp/cublas-xt-evaluation-version - but this needs membership of the CUDA Registered Developer Program. Sign up here: https://developer.nvidia.com/registered-developer-program