Comparing "Derivative" with "SymPy" :

- everything "Derivative" calculates uses Python/SymPy, but "Derivative" is a lot easier to use;

- launching SymPy and typing "simplify(diff(sqrt(x/(1+x**3)),x,x))" is easy, but "Derivative" has time measuring, shows non-calculated derivative, has zoom in/out for output, many simplification options, output types, etc;

- SymPy does not know how to calculate gradient, divergence, curl and laplacian, it needs to be programmed to do it, like it is done in "Derivative" (see the end of the source code);

- it is better to use SymPy (interactive shell, i.e., tapping the SymPy icon) when it is needed a sequence of calculations, like derivate some expression, use the result in a equation, solve it, take the result and replace some variables, etc.

The last item will be further addressed because I hope to release "MathSymPy", a SymPy front-end in Python/Qt, mixing some features (easy of use of graphical user interface, many options, etc) of "Integral", "Derivative", etc, with the flexibility of the iSymPy interactive shell. In the best scenario, MathSymPy will be first released in 2-3 months for Maemo 4 & 5 and then MeeGo 1.2 Harmattan.