Gnucap is the Gnu Circuit Analysis Package.
The primary component is a general purpose circuit simulator. It performs nonlinear dc and transient analyses, fourier analysis, and ac analysis. It is fully interactive and command driven. It can also be run in batch mode or as a server.
Spice compatible models for the MOSFET (level 1-7), BJT, and diode are included in this release.Gnucap is not based on Spice, but some of the models have been derived from the Berkeley models.Unlike Spice, the engine is designed to do true mixed-mode simulation. Most of the code is in place for future support of event driven analog simulation, and true multi-rate simulation.
If you are tired of Spice and want a second opinion, you want to play with the circuit and want a simulator that is interactive, you want to study the source code and want something easier to follow than Spice, or you are a researcher working on modeling and want automated model generation tools to make your job easier, try Gnucap.