Copy/paste from http://www.redhat.com/archives/rhl-l.../msg02664.html:
Maxima is a version of the MIT-developed MACSYMA system, modified to run under Common LISP. It is an interactive expert system and programming environment for symbolic and numerical mathematical manipulation. Written in LISP, it allows differentiation, integration, solution of linear or polynomial equations, factoring of polynomials, expansion of functions in Laurent or Taylor series, computation of Poisson series, matrix and tensor manipulations, and two- and three-dimensional graphics.
Procedures may be written using an ALGOL-like syntax, and both LISP-like functions and pattern matching facilities are provided. Files containing maxima objects may be read from and written to disk files. Pre-written maxima commands may be read from a file and executed, allowing batch-mode use.
Sounds to me like a Maple-equivalent... which has a bunch of free clones
Anyway, Maxima is in the universe repositories
sudo apt-get install maxima