The MPFR library is a C library for multiple-precision floating-point computations with correct rounding.
Octave is a public domain clone of matlab. It is about 95% compatible with Matlab.
OpenBLAS is an optimized BLAS library based on GotoBLAS2 1.13 BSD version.
ParMETIS is an MPI-based parallel library that implements a variety of algorithms for partitioning unstructured graphs, meshes, and for computing fill-reducing orderings of sparse matrices.
PETSc, pronounced PET-see (the S is silent), is a suite of data structures and routines for the scalable (parallel) solution of scientific applications modeled by partial differential equations.
PROMISE is a tool to auto-tune the precision of floating-point variables in numerical codes.
R is a free software environment for statistical computing and graphics.
ROOT is a data analysis framework.