Graph is described as 'open source application used to draw mathematical graphs in a coordinate system. Anyone who wants to draw graphs of functions will find this program useful. The program makes it very easy to visualize a function and paste it into another program' and is an app in the Education & Reference category. There are more than 25 alternatives to Graph for a variety of platforms, including Windows, Mac, Linux, Online / Web-based and iPhone. The best alternative is R (programming language), which is both free and Open Source. Other great apps like Graph are GeoGebra (Free), SageMath (Free, Open Source), Matplotlib (Free, Open Source) and Microsoft Mathematics (Free).
Is a powerful, easy-to-use, equation plotter with numerical and calculus features: Win32 screen shot. Graph Cartesian functions, relations, and inequalities, plus polar, parametric, and ordinary differential equations. Up to 999 graphs on screen at once.
Graph toy is an interactive graph visualizer using mathematical functions. Based on the original Graphtoy by Inigo Quilez, it provides some helpful additions including an easy way to share graph links.