GNU Octave is a program meant for numerical computations and will allow the user to display a command line interface to be able to solve numerical issues that are either linear of nonlinear.
The software has add ons that can allow you to work on algebra issues, try to understand and get the roots of nonlinear equations, to add fuctions, to work and change polynomials, to work on differential-algebraic equations.
You can easily customize its interface to make it respond to your needs.
GNU Octave is free to distribute and use as it is an open source program.
You can even participate in the enhancement of the program as you may make changes to the program itself to try to make it better.
It is quite a bulky program and not every pc will be able to bear the capacity of this program.