Math Links
Desmos
Desmos is an online graphing calculator. It is a free tool that can be used to plot and graph data and functions. One useful interactive feature of Desmos allows you to see how a graph changes when you manipulate the function's variables. Desmos is an extremely simple website to navigate and very user-friendly.
Mathematica
Mathematica is a great tool to help with visualization of functions. This application can graph functions in 3D, display the direction fields of a vector, and much more. While the programming language can be difficult to learn, it is worth it in the end.