Wolfram is a great website that has been offering educational tools for teachers and students all around the world.
Wolfram has recently added Wolfram Education Portal. This is basically a free to use online tool that helps teachers with the Math courses they are teaching. It focuses specifically on Algebra and Calculus. It is completely free and has a student friendly interface. This portal also provides teachers and students with the opportunity to use interactive and dynamic course materials developed with Wolfram Alpha and Mathematica to enhance the teaching and learning experience. Among the resources you can find there are ; Lesson plans, e-Textbooks, and demonstration tools such as graphs, widgets and calculators.