Giac/Xcas - Free computer algebra system
GeoGebra CAS Calculator - Free online algebra calculator from GeoGebra: solve equations, expand and factor expressions, find derivatives and integrals
Geometry Pad - Geometry Pad is a dynamic geometry application for iPad and Android tablets.
Dr. Geo - Dr. Geo, a software to design & manipulate interactive geometric sketches.
GnuPlot - Gnuplot is a portable command-line driven interactive data and function plotting utility.
Autograph - Autograph is a dynamic PC program operating in 3 modes: 1D - Statistics & Probability