qucs

Qucs is an integrated circuit simulator which means you are able to setup a circuit with a graphical user interface (GUI) and simulate the large-signal, small-signal and noise behaviour of the circuit. After that simulation has finished you can view the simulation results on a presentation page or window.
Qucs, briefly for Quite Universal Circuit Simulator, is a circuit simulator with graphical user interface (GUI). The GUI is based on Qt® by Trolltech®. The software aims to support all kinds of circuit simulation types, e.g. DC, AC, S-parameter, Harmonic Balance analysis, noise analysis, etc.
Qucsator, the simulation backend, is a command line circuit simulator. It takes a network list in a certain format as input and outputs a Qucs dataset. It has been programmed for usage in the Qucs project but may also be used by other applications.So far we were working on the GUI and on some basic simulation features. In fact there is now a kind of useful user interface for setting up schematics and presenting simulation results in various types of diagrams. DC, AC, S-parameter, noise and transient analysis is possible, mathematical equations and use of a subcircuit hierarchy are available. Anyway, a lot of work has to be done and thus we are looking for people who want to support the project.