GeoGebra is both online and an app you can download for your phone or computer. It is great for any math teacher or student. With GeoGebra, you can graph functions and shapes and so much more. It's good for students because it gives them tangible examples of the confusing functions that they just stare at during class. You can also create groups for your students to use so it can become a group effort on projects or students can take the lesson home with them.