GeoGebra - GeoGebra is free and multi-platform dynamic mathematics software for learning and teaching.
GnuPlot - Gnuplot is a portable command-line driven interactive data and function plotting utility.
Geometry Pad - Geometry Pad is a dynamic geometry application for iPad and Android tablets.
Giac/Xcas - Free computer algebra system
Autograph - Autograph is a dynamic PC program operating in 3 modes: 1D - Statistics & Probability
Dr. Geo - Dr. Geo, a software to design & manipulate interactive geometric sketches.