Core Plot!

GeoGebra is free and multi-platform dynamic mathematics software for learning and teaching. It has received several educational software awards in Europe and the USA.

Gnuplot is a portable command-line driven interactive data and function plotting utility. It was originally intended as to allow scientists and students to visualize mathematical functions and data. It does this job pretty well, but has grown to support many non-interactive uses, including web scripting and integration as a plotting engine for third-party applications like Octave. Gnuplot supports many types of plots in either 2D and 3D. It can draw using lines, points, boxes, contours, vector fields, surfaces, and various associated text. It also supports various specialized plot types. »

matplotlib is a python 2D plotting library which produces publication quality figures in a variety of hardcopy formats and interactive environments across platforms. matplotlib can be used in python scripts, the python and ipython shell (ala MATLAB®* or Mathematica®†), web application servers, and six graphical user interface toolkits.

SciDAVis is a free application for Scientific Data Analysis and Visualization. It's an application aimed at data analysis andpublication-quality plotting. It combines a shallow learning curve andan intuitive, easy-to-use graphical user interface with powerfulfeatures such as scriptability and extensibility. Quite extensive manual can be found here: http://scidavis.sourceforge.net/help/manual/index.html

OmniGraphSketcher helps you make elegant and precise graphs in seconds, whether you have specific data to visualize or you just have a concept to explain. Specifically designed for reports, presentations, and problem sets where you need to produce sharp-looking graphs on the fly, OmniGraphSketcher combines the data plotting power of charting applications with the ease of a basic drawing program.

GrafEq (pronounced “graphic”) is an intuitive, flexible, precise and robust program for producing 2D graphs and plots of explicit and implicit equations and inequalities.

pro Fit is a Macintosh (Mac OS) application for data/function analysis, plotting, and curve fitting. It is used by scientists and engineers to analyze their measurements and the mathematical models they use to describe them.

DPlot graphing software lets scientists and engineers graph, plot, analyze, and manipulate data.

Timeplotters are command-line tools for visualizing temporal data, especially useful for visualizing data from ad-hoc program logs to help you spot patterns and anomalies that you would not spot otherwise (by just watching how the program works, or by looking at the logs with the naked eye).

Aveloy Graph is an application for graph creation / data visualization - fast, easy to use and interactive.

Layers based charts library for iOS