Octave is a free program for doing math computations, especially ones related to linear algebra.  You can experiment with parts of Octave online at the following site:

http://lavica.fesb.hr/octave/octave-on-line_en.php

Some hints about using Octave can be found at Octave’s online user’s manual

http://www.gnu.org/software/octave/doc/interpreter/