ZeGrapher is a free and open source software for plotting mathematical objects (functions, sequences, parametric equations) and experimental data on the plane. This software is intended to be as easy to use as possible, suitable for high school students.
MobileMath is a software written by using J2ME technolology. It turns mobile into calculator supporting many operations such as : evaluate expression, plotting, differentiate & integrate expression... It can run on any mobiles supporting Java.