Grapher Lite is a math function plotter that you can use to draw nice figures. In a single line, compose at most 10 functions of a single variable (x), separated by semi-colon(s) and press enter to plot them. You may then export the drawn figure to a PNG image file. You can also load an image file as a background. Different standard math functions are included (please have a look at the list of math functions).
In Release 7, you can now share the drawn PNG to other applications.