Desmos is the next generation of the graphing calculator. Desmos is an easy-to-use but powerful graphing tool that handles graphing, variable sliders, tables, statistics, zooming, points of interest, inequalities, and more. And best of all: it's completely free.
GeoGebra GeoGebra is an interactive, dynamic math program that provides tools for geometry, algebra, spreadsheets, graphing, statistics and calculus. Over a half million shared resources are available here.