See also DebianScienceMaxima.
Maxima -- Web: http://www.ma.utexas.edu/users/wfs/maxima.html
Description
A fairly complete computer algebra system, especially for formal calculus.
Presentation in French :
http://logiciels-libres-cndp.ac-versailles.fr/article.php3?id_article=54&var_recherche=maxima