This is the M.I.T. link for FastCap, FastHenry and FastImp *nix 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.
Whiteley Research offers a completely free graphical editor and design tool for integrated circuit mask layout, schematic capture, and much more, and a companion Spice circuit simulation tool, for *nix and Windows. All the software is also available in Open Source. Parasitic extraction is available through FasterCap, FastCap and FastHenry.
Ngspice is an open-source (BSD license), free, multi-platform (Windows, Linux, MacOS), analog / digital Spice-based simulator.
It is an evolution of the original Berkeley SPICE3F5, integrated with XSPICE
(for mixed-signal simulation), and including TLCSpice (a TCL/TK interface).
Ngspice is also integrated in KiCad and in the gEDA suite of Electronic Design Automation tools available for Linux and MacOS.
Qucs is a promising open-source (GLP license), free, multi-platform (Windows, Linux, MacOS) circuit simulator. Qucs provides a GUI for schematic entry and for showing simulation results in various types of diagrams. It supports DC, AC, S-parameter, noise and transient analysis is possible. It allows mathematical equations and use of a subcircuit hierarchy (with parameterised subcircuits) are available. Qucs can also import existing SPICE models.
LTSpice is a free, analog / digital Spice-based simulator for Windows with schematic entry and waveform post-processor from Linear Technology. Albeit not open source, it is a very friendly tool, with no size limits, to run circuit simulations on the results of your field solvers extractions.
FreeCAD is a parametric 3D CAD modeler. Parametric modeling allows you to easily modify your design by going back into your model history and changing its parameters. FreeCAD is open-source, multi-platform and highly customizable, scriptable and extensible. Our ElectroMagnetic workbench is based on FreeCAD.
KLayout is a high performance layout viewer and editor, free and open source. The de-facto viewer for GDS files. A must have.
KiCad is a cross-platform and Open Source Electronics Design Automation Suite. It also provides an embedded electrical circuit simulator using ngspice as the simulation engine.
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.
The Free Silicon Foundation is a nonprofit organization with the scope of promoting: 1. Free and Open Source (FOS) CAD tools for designing integrated circuits, 2. the sharing of hardware designs and libraries, 3. common standards, 4. the freedom of users in the context of silicon integrated circuits. It is the main sponsor of the Free Silicon Conference (FSiC)