"SageMath is a free open-source mathematics software system licensed under the GPL. It builds on top of many existing open-source packages: NumPy, SciPy, matplotlib, Sympy, Maxima, GAP, FLINT, R and many more. Access their combined power through a common, Python-based language or directly via interfaces or wrappers... Mission: Creating a viable free open source alternative to Magma, Maple, Mathematica and Matlab."
"Wolfram|Alpha introduces a fundamentally new way to get knowledge and answers—
not by searching the web, but by doing dynamic computations based on a vast collection of built-in data, algorithms, and methods."
"R is a language and environment for statistical computing and graphics. It is a GNU project which is similar to the S language and environment... R can be considered as a different implementation of S. There are some important differences, but much code written for S runs unaltered under R... R provides a wide variety of statistical (linear and nonlinear modelling, classical statistical tests, time-series analysis, classification, clustering, …) and graphical techniques, and is highly extensible."