I\'m learning the MATLAB language and would like to have some kind of free environment to experiment with. The MATLAB environment provided by MathWorks is commercial. There
Other users have given you the examples that I would have suggested - Octave and Scilab. Of the two, I would say that Scilab is more powerful BUT Octave tries really hard to be source compatible with standard MATLAB and Scilab does not.
So, if your aim is to experiment with a MATLAB like language and learn skills that you will eventually be able to transfer over to MATLAB then I suggest that you stick with Octave.