GnuPlot!

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.

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.

Microsoft Mathematics is a desktop graphing calculator that can help you visualize and see mathematical concepts as you’ve never seen them before. Microsoft Mathematics includes ink handwriting support to recognize hand-written problems.

A beautiful, innovative, and modern online graphing calculator.

Giac/Xcas is a free computer algebra system for Windows, Mac OS X and Linux/Unix (license GPL3, for commercial dual-license contact us).

Dash Reports is a versatile and light weight reporting solution. It allows users and administrators to create a large range of reports driven by SQL databases.

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

GraphCalc is an all-in-one solution to everything from everyday arithmetic to statistical analysis, from betas to Booleans, from cubes to calculus, from decimals to derivatives. GraphCalc combines all the features of a professional mathematics package with the simplicity of an easy to learn windows interface. It provides user-friendly help and tutorials to guide you through the easy and fun process of mastering GraphCalc.

DataGraph is a simple and powerful graphing application for Mac OS X. It is a great companion for Excel, Numbers or any of the big statistical packages.

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.

ksar is a sar graphing tool that can graph for now linux,mac and solaris sar output. sar statistics graph can be output to PDF or jpg/png/csv/txt.