maxima: maxima (free CAS)
maxima: 
maxima: maxima is a free Computer Algebra System for symbolic and numeric 
maxima: mathematics. It supports ifferentiation, integration, Taylor series, 
maxima: Laplace transforms, ordinary differential equations, systems of linear
maxima: equations, polynomials, and sets, lists, vectors, matrices & tensors.
maxima: Maxima yields high precision numeric results by using exact fractions,
maxima: arbitrary precision integers, and variable precision floating point 
maxima: numbers. Maxima can plot functions and data in two & three dimensions.
maxima: 
maxima: http://maxima.sourceforge.net/