FormulaDesk Math is described as 'Excel add-in that brings real symbolic math to Excel. View formulas as equations, plot formulas…instantly. All the tools that engineers and students need every day, now inside Excel' and is an app in the Education & Reference category. There are more than 50 alternatives to FormulaDesk Math for a variety of platforms, including Windows, Linux, Mac, Microsoft Office Excel and Online / Web-based. The best alternative is Mathematica. It's not free, so if you're looking for a free alternative, you could try SciPy & Numpy or Maxima. Other great apps like FormulaDesk Math are fxSolver (Free), wxMaxima (Free, Open Source), ASAP Utilities (Paid) and Xcos (Free, Open Source).
Maxima is a system for the manipulation of symbolic and numerical expressions, including differentiation, integration, Taylor series, Laplace transforms, ordinary differential equations, systems of linear equations, polynomials, and sets, lists, vectors, matrices, and tensors.
wxMaxima is a document based interface for the computer algebra system Maxima. wxMaxima uses wxWidgets and runs natively on Windows, X11 and Mac OS X. wxMaxima provides menus and dialogs for many common maxima commands, autocompletion, inline plots and simple animations.
SymPy is a Python library for symbolic computation. The stated goals of the library are to become a full-featured computer algebra system and to keep a simple code base to promote extensibility and comprehensibility.