A ComputerAlgebraSystem is a system that performs all the tedious mucking about with formulae and equations for you. Generally they can simplify, factor, integrate, differentiate, solve, expand, and more. They work symbolically, not numerically, so they can tell you that x^2+3x+2 is (x+1)(x+2), and not simply tell you that the values of x that satisfy x^2+3x+2=0 are -1 and -2.
Examples include (in no particular order):