OpenBLAS
An optimized BLAS library based on GotoBLAS2 1.13 BSD version. [BSD 3-clause] website
C/C++ › Math: “An optimized BLAS library based on GotoBLAS2 1.13 BSD version. [BSD 3-clause] website”
Fortran › Math Libs: “one of the fastest open source BLAS libraries available. Almost as fast as Intel MKL.”