Here is a site with several online numerical math tools:

Numerical Mathematics Tools

The tools are for immediate online use, although I suppose they could be saved for offline use as well (since they are written in Javascript).

Some of the tools include utilities for solving the Quadratic, Cubic, and Quartic Equations; solving N Equations in N Unknowns; Eigenvalues and Eigenvectors; and more.

Regards.

David