Giac/Xcas is described as 'free computer algebra system for Windows, Mac OS X and Linux/Unix (license GPL3, for commercial dual-license contact us)' and is an app in the Education & Reference category. There are more than 25 alternatives to Giac/Xcas for a variety of platforms, including Windows, Linux, Mac, Online / Web-based and Android. The best alternative is Qalculate!, which is both free and Open Source. Other great apps like Giac/Xcas are GeoGebra (Free, Open Source), MATLAB (Paid), Mathematica (Paid) and Windows Calculator (Free, Open Source).
Axiom is a general purpose Computer Algebra system. It is useful for research and development of mathematical algorithms. It defines a strongly typed, mathematically correct type hierarchy. It has a programming language and a built-in compiler.
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.
WordMat is an add-on to Microsoft Word which creates a tab with math functionality. Part of the Math functionality is provided by other open-source applications like Maxima, GeoGebra, Graph and GnuPlot.
Omni Calculator is a web/mobile calculator that solves concrete problems such as mortgage payment, gross margin, body mass index, break-even point, etc. It's very user-friendly, flexible and usable on web, mobile and as an embeddable web widget.
SymbolicC++ uses C++ and object-oriented programming to develop a computer algebra system. Object-oriented programming is an approach to software design that is based on classes rather than procedures. This approach maximizes modularity and information hiding.