The Schwarz-Christoffel Toolbox for MATLABThe SC Toolbox is a problem-solving environment for computation and interaction with conformal maps to regions bounded by polygons, including unbounded regions, logical quadrilaterals, and channels. It includes a module for the solution of the Laplace equation on such regions with piecewise constant boundary conditions, to ten digits or more in seconds.
The Chebfun systemThe Chebfun system is a free MATLAB package hosted ax Oxford University for numerical computation with functions. My interest and contribution to the system is mostly in the chebop class. A chebop is an abstraction of a numerically realized differential or integral operator. Using familiar MATLAB syntax such as \ and eigs, solutions to linear differential boundary value or eigenvalue problems can be obtained with ten or more digits of precision automatically.
Other MATLAB software
There are a few others listed in my MATLAB Central area.