TouchPlot is a grapher with touch abilities, designed for the Apple's iPhone and iPod touch. It aims at drawing graphs of user defined functions, parametric curves with cartesian or polar coordinates, semi-log and log graphs. It also draws solutions to ordinary differential equations, with or without a vector field, implicit curves,
equations, inequations solutions, contourplots...
It can also plot surfaces with equation z = F(x,y) with nice touch gestures for dragging, rescaling, and the accelerometer is used to tilt the graph.
The current version of TouchPlot is now 4.0. If you own a previous version of TouchPlot, make sure you update it (updates are free).
The version 4.0 received an alternative editor, with an algebraic mode that is much easier to use for beginners. The previous mode (quite powerful and efficient once you get accustomed to it) is still there as an option, to be activated in TouchPlot application preferences.
To get some ideas of what you can do with TouchPlot, I urge you to have a look at the videos there or through youtube following this link.
To go to the iTunes page for TouchPlot, follow this link : TouchPlot in the AppStore