Desmos - Graphic Calculator
Desmos is a free graphing site with a lot to offer math and science teachers. They don't only have a great free Graphing Calculator Links to an external site., but offer other graphing functions.
They have a free Math Tutorial Links to an external site.section just for math teachers.
Graph functions, plot tables of data, evaluate equations, explore transformations, and much more – for free!
This a free, embeddable media, but does require a subscription to access.