Here's a list of some of the topics for which Scilab can be used :

1) To solve addition, subtraction, multiplication, division

2) To solve polynomials, finding their roots

3) Integration, derivative

4) Exponential function, Square roots function

5) To see the plot of a system

6) Operations on Matrices

7) Operations on Vectors

8) Find GCD and LCM

9) Mean, variance, standard deviation and may more such topics