Yacas: An easy to use, general purpose Computer Algebra System.
Developer: Ayal Pinkus
License: GNU GPLv2
Yacas (Yet Another Computer Algebra System) is a small and highly flexible general-purpose computer algebra system and programming language. The language has a familiar, C-like infix-operator syntax. The distribution contains a small library of mathematical functions, but its real strength is in the language in which you can easily write your own symbolic manipulation algorithms. The core engine supports arbitrary precision arithmetic, and is able to execute symbolic manipulations on various mathematical objects by following user-defined rules.
You can use Yacas directly from the web site as a Java applet (it runs inside your browser without needing a connection to a remote server). This means that no additional software needs to be installed (other than a free Java environment if this is not installed yet).
Yacas can also be downloaded. The download contains an off-line version of Yacas, a native executable that can run on your computer. The menu entry starts the console of the "Yacas calculation center".