YACAS (Yet Another Computer Algebra System) is a small and highly flexible computer algebra language. It contains a library of mathematical functions, but its real strenght is in the language in which you can easily write your own symbolic manipulation algorithms.It supports arbitrary precision arithmetic.
Current Version: 1.0.47
Download YACAS here.
Download MorphOS version.
Go to yacas homepage: http://www.xs4all.nl/~apinkus