FastCap and FastHenry M.I.T. source code distribution
This is the M.I.T. link for FastCap and FastHenry Unix source files distribution.
This is the direct link to the M.I.T. CAD group, where FastCap and FastHenry were developed. Throught this link you can reach the pages containing the original docs and the papers presenting the algorithms implemented in the software.
LTSpice IV is a free, analog / digital Spice-based simulator with schematic entry and waveform post-processor from Linear Technology. Very useful free tool to run circuit simulations on the results of your field solvers extractions.
Whiteley Research offers a graphical editor and design tool for integrated circuit mask layout, schematic capture, and much more, and a companion circuit simulation tool. Parasitic extraction is available through FasterCap, FastCap and FastHenry.
Scilab is free and open source software for numerical computation providing a powerful computing environment for engineering and scientific applications. It is a very valid replacement for Matlab.
Maxima is an open source, free system for the manipulation of symbolic and numerical expressions. It is the right companion for SciLab.