Open source math software

Here I am again. Looking for open source alternatives to expensive software. This time, alternatives to Mathematica, MatLab, and S/S+.

If you don't have the bucks, a decent alternative to Mathematica is Maxima. Maxima had its origins to DOE Macsyma which was the first among the modern computer algebra systems like Maple and Mathematica. Maxima does symbolic integration, 3D plotting, and ODE solving among many other features. It is available for Windows and Linux systems.

SciLab on the other hand is a very good alternative to MatLab. Scilab is a scientific software package for numerical computations. It provides a powerful open computing environment for engineering and scientific applications. SciLab is available for Windows, Linux, HP-UX, and Solaris platforms.

Looking for an open source statistical software? I recommend R, a very sophisticated open source statistical package. R uses a dialect of the S/S+ statistical software package. R is available for Windows, Linux, and MacOS systems.

Of course Mathematica and MatLab are great software packages. However, they are just too expensive for me.