Here is a list of geometric algebra software that I know. If you have software not on this list, send me a link to your webpage by filling up the Comment Form below.
GluCat: Generic library of universal Clifford algebra templates by Carl Brannen
GABLE: A Matlab Geometric Algebra Tutorial 2007 by Leo Dorst and Stephen Mann
Interactive and animated Geometric Algebra with Cinderella 2004 by Ekhard Hitzer