Open source Mathematics

FreeMat

FreeMat is a free environment for rapid engineering and scientific prototyping and data processing. (GPL)

Linux - FreeBSD - Windows - MAC OS X

Genius

Genius is useful both as a simple calculator and as a research or educational tool. The syntax is very intuitive and is designed to mimic how mathematics is usually written. (GPL)

Linux

Getfem++

The Getfem++ project focuses on the development of a generic and efficient C++ library for finite element methods. (GPL)

Linux - MAC OS X - Windows

GNU Octave

GNU Octave is a high-level language, primarily intended for numerical computations. (GPL)

Linux - FreeBSD - Windows - MAC OS X

Maxima

Maxima is a fairly complete computer algebra system written in lisp with an emphasis on symbolic computation. (GPL)

Linux - FreeBSD - Windows - MAC OS X

SAGE

SAGE is a viable free open source alternative to Magma, Maple, Mathematica, and Matlab. (GPL)

Linux - FreeBSD - Windows - MAC OS X

Scilab

Scilab is a scientific software package for numerical computations providing a powerful open computing environment for engineering and scientific applications. (GPL)

Linux - Windows

SpeedCrunch

SpeedCrunch is a fast, high precision and powerful desktop calculator. (GPL)

Linux - FreeBSD - Windows - MAC OS X

8 applications