GeoGebra CAS Calculator - Free online algebra calculator from GeoGebra: solve equations, expand and factor expressions, find derivatives and integrals
Dr. Geo - Dr. Geo, a software to design & manipulate interactive geometric sketches.
Giac/Xcas - Free computer algebra system
Geometry Pad - Geometry Pad is a dynamic geometry application for iPad and Android tablets.
GnuPlot - Gnuplot is a portable command-line driven interactive data and function plotting utility.
Graphmatica - Is a powerful, easy-to-use, equation plotter with numerical and calculus features: