Gnucap Alternatives

Ngspice is a mixed-level/mixed-signal circuit simulator.

LTspice® is a high performance SPICE simulation software, schematic capture and waveform viewer with enhancements and models for easing the simulation of analog circuits.

OrCAD PSpice technology provides the best, high-performance circuit simulation to analyze and refine your circuits, components, and parameters before committing to layout and fabrication

Qucs, briefly for Quite Universal Circuit Simulator, 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.

As IC geometries continue to shrink, the need for an accurate circuit simulator is critical.

Electronic circuit simulation for the Mac, support and downloads site.

Animated electronic circuit simulator using ideal components to visualize voltage and current.

Xyce is an open source, SPICE-compatible, high-performance analog circuit simulator, capable of solving extremely large circuit problems by supporting large-scale parallel computing platforms.

Multisim is industry standard SPICE simulation and circuit design software for analog, digital, and power electronics in education and research.

Solve Elec is a free educational program to draw and analyze electrical circuits.

A Cross Platform and Open Source Electronics Design Automation Suite

Mixed Mode Simulation

Proteus - Proteus is a great electrical suite for circuit simulation purposes. You can simulate a single processor or multiple ones at the same time. The application is a great alternative for Virtual System Modelling.