GNU Octave

GNU Octave is a free and open-source software and high-level interactive language for numerical computations.

Octave packages
Octave's functionality (i.e. selection of functions available to the user in octave) is extended via octave-packages [1], usually provided by octave-forge [2]. Gentoo's portage tree contains the ebuild "app-portage/g-octave" which allows the user to generate and install ebuilds for octave-packages from Octave-Forge.

[1] http://octave.sourceforge.net/packages.php

[2] http://octave.sourceforge.net/index.html