http://www.scilab.org/
Scilab is a mathematical software for numerical computation which is similar to Matlab. This is very useful for physical computations. It is developed by INRIA and École nationale des ponts et chaussées (ENPC). It can be downloaded for free at the above links. See also the license. The syntax of scilab is similar but not compatible to Matlab. However we can convert Matlab format to Scilab format easily using a converter included in the Scilab. There is also a nice package called Scicos for modeling and simulation. I use Scilab mainly for plotting, data processing, numerical calculations and solving matrix equations.
