Maxima is a GPL
'd Common Lisp mathematics application
for computer based algebra (an implementation of MIT
system). Until recently, it was maintained by William Schelter at http://www.ma.utexas.edu/maxima.html
. He passed away in 2001 and since then a group of developers co-ordinated around http://maxima.sourceforge.net
have been working on it.
How to Install Maxima shows how you can build Maxima with CLISP and also demonstrates how to make Maxima use geomview, rendering amazing graphics via MesaGL. Also, how to set up TeXmacs with it.
Maxima can also be used from Common Lisp programs as a library. See the section Lisp and Maxima in the Maxima manual for more information.