Gnuplot is a portable command-line driven graphing utility that was originally created to allow scientists and students to visualize mathematical functions and data interactively, but has grown to support many non-interactive uses such as web scripting. It is a freeware graph plotting application that's powerful, efficient and helpful.
Here are some screenshots to illustrate the features and user interface of this application:
Qalculate
GeoGebra
GeoGebra Portable
Advanced Trigonometry Calculator
Maxima