Qucs-S Alternatives

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.

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

KTechLab is an IDE for microcontrollers and electronics.

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.

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

A virtual simulation environment for electronic circuits with support of digital and analog devices.

Digital Electronics Education and Design Suite

an emulator for the Arduino platform by Greg Hewgill

Xcos is a graphical editor to design hybrid dynamical systems models.

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

It is a circuit simulator on a virtual breadboard.

Kepler is a free open-source software system for designing, executing, reusing, evolving...