Briefly summarize some numerical library here. It looks there are too many useful tools. Either for parallel computing or for matrix, numerical calculating and plotting.
MatPlotLib: it seems to be the most awesome plotting tool among this list
PGPlot: C library, also have binding in Perl, Python,Ruby
PLPlot: cross-platform plot library, also have binding in Perl
MPI Ruby: MPI Ruby binding
PyMPI: MPI integrated Python interpreter
MPI for Python Python MPI binding
Simple Remote Python : SrPy
Perl Data Language: difficult to be categorized. Including calculating, plotting together. include FFTW, PGPlot, PLPlot, and many data processing tool such as HDF. Awesome Environment!
MPMath: Multi-Precision math functions collection.
LibFFTW, also have binding in Perl, Ruby
GNU Scientific Library: C library, also have bindings in Ruby named Ruby/GSL and Ruby-GSL. and Python
RSRuby: bridge between Ruby and R
Ruby for Science