GraphCalc!

Wolfram Alpha is a "Computational Knowledge Engine" - different from a search engine, it answers factual queries directly by computing the answer from structured data, rather than providing a list of documents or web pages that might contain the answer.

Mathematica is a computational software program used widely in scientific, engineering, and mathematical fields and other areas of technical computing.

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. »

Qalculate! is a multi-purpose desktop calculator for GNU/Linux and Windows. It is small and simple to use but with much power and versatility underneath. Features include customizable functions, units, arbitrary precision, plotting, and a user-friendly interface (KDE or GTK+).

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.

Windows Calculator, commonly known as Calculator from the application's title bar, is a calculation application included in all versions of the Microsoft Windows operating system. It can be activated by the command "calc" on most Windows systems.

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

MathStudio, formerly SpaceTime, is the most comprehensive math app available for mobile devices. Whether you need a simple calculator to do your finances or a replacement for your TI graphing calculator, MathStudio is the most powerful and versatile calculator available on the App Store and Android Market.

ASCEND is a free open-source software program for solving small to very large mathematical models. ASCEND can solve systems of non-linear equations, linear and nonlinear optimisation problems, and dynamic systems expressed in the form of differential/algebraic equations.

WIRIS cas is an online platform for mathematical calculations designed for education. You can access a powerful calculation toolbar through an HTML page that includes integrals and limits calculation, function graphing in 2D or 3D and symbolic matrices manipulation, among others.