An open-source, free circuit simulator

&gt; Qucs is a GPL circuit simulator. And if you want the GUI option, you might want to try out QucsStudio, which uses Qucs under the hood, and is free to use, but binary-only.<p>Huh? I used Qucs many moons ago and it definitely was complete with GUI.<p><a href="https:&#x2F;&#x2F;qucs.sourceforge.net&#x2F;screenshots.html" rel="nofollow noreferrer">https:&#x2F;&#x2F;qucs.sourceforge.net&#x2F;screenshots.html</a><p>Unfortunately Qucs is unmaintained, probably doesn&#x27;t compile anymore on newer distributions and its binaries were therefore removed from many repositories. Another problem: Qucs was released as GPL while QucsStudio, which uses its sources, has been kept closed by the authors; I smell a GPL violation here.

It&#x27;s a shame that circuit simulators, especially those derived from SPICE, have tended toward closed-source. It&#x27;s nice that there are several free-as-in-beer options available, but a good lesson in the consequences of permissive open-source licenses. SPICE predates copyleft licensing, so software that was once open has disappeared into proprietary versions.<p>LTspice (sponsored by Analog Devices) is closed-source. The recently-released QSpice (sponsored by Qorvo) also closed-source. QucsStudio was taken closed-source by Qucs&#x27; original author, and he&#x27;s not commented on his intentions in this decision.<p>Big companies typically open-source software when it&#x27;s not part of their strategic business value, and offers community engagement benefits and good press. LTspice is kind of an advertisement for AD&#x27;s chips. AD and Qorvo aren&#x27;t remotely in the software and EDA business, so their decision to keep them closed is even more puzzling, but I guess the instinct of hardware companies is guard everything.

On windows there is LTSpice which is free, has a lot of models, but not open source and ngspice which is open source but it does not have a GUI (although i heard that it can be used with KiCAD).<p>So i really don&#x27;t underestand, what would be the advantage of using Qucs ?

As an amateur I always default to CircuitJS, it&#x27;s a great learning resource<p><a href="https:&#x2F;&#x2F;www.falstad.com&#x2F;circuit&#x2F;circuitjs.html" rel="nofollow noreferrer">https:&#x2F;&#x2F;www.falstad.com&#x2F;circuit&#x2F;circuitjs.html</a>

You should consider using qucs-s <a href="https:&#x2F;&#x2F;ra3xdh.github.io&#x2F;" rel="nofollow noreferrer">https:&#x2F;&#x2F;ra3xdh.github.io&#x2F;</a> a fully open-source fork of qucs still currently maintained and improved.

When talking about open source tools, here are some:<p>KiCad may be used as a schematic entry tool for ngspice, especially for discrete or PCB-based electronics. You may watch several simulation examples (including oscillators) here: <a href="https:&#x2F;&#x2F;forum.kicad.info&#x2F;t&#x2F;simulation-examples-for-kicad-eeschema-ngspice&#x2F;34443" rel="nofollow noreferrer">https:&#x2F;&#x2F;forum.kicad.info&#x2F;t&#x2F;simulation-examples-for-kicad-ees...</a>. KiCad integrates ngspice internally, but may also provide external ngspice with netlists for simulation.<p>Another GUI to ngspice is XSCHEM, especially useful for IC design work (see <a href="https:&#x2F;&#x2F;xschem.sourceforge.io&#x2F;stefan&#x2F;index.html" rel="nofollow noreferrer">https:&#x2F;&#x2F;xschem.sourceforge.io&#x2F;stefan&#x2F;index.html</a>). Device models are available by the Open Source PDKs from Google&#x2F;Skywater, Google&#x2F;GF, or IHP. A growing community is supporting digital, analog or mixed-signal design flows.<p>QUCS-S (<a href="https:&#x2F;&#x2F;ra3xdh.github.io&#x2F;" rel="nofollow noreferrer">https:&#x2F;&#x2F;ra3xdh.github.io&#x2F;</a>) is a GUI for ngspice or XyCE.<p>Indeed device models have to be added manually to the devices in the circuit schematic, when invoking ngspice via KiCad or QUCS-S, except for some basic devices with integrated models. Models are provided by device makers, distributors or web sites like this one: <a href="https:&#x2F;&#x2F;ngspice.sourceforge.io&#x2F;modelparams.html" rel="nofollow noreferrer">https:&#x2F;&#x2F;ngspice.sourceforge.io&#x2F;modelparams.html</a> .

Can it simulate oscillators? Many of the lower end or cheaper systems fall apart when it comes to modelling real world radios. Probably because in reality everything is a bit capacitive&#x2F;inductive and there is a noise floor at any given frequency.

Wokwi is free open source and neat with an MIT license <a href="https:&#x2F;&#x2F;github.com&#x2F;wokwi&#x2F;avr8js">https:&#x2F;&#x2F;github.com&#x2F;wokwi&#x2F;avr8js</a> <a href="https:&#x2F;&#x2F;wokwi.com" rel="nofollow noreferrer">https:&#x2F;&#x2F;wokwi.com</a>

surprising to see nobody&#x27;s mentioned ngspice, wr-spice, or omedit (the openmodelica editor), all of which are open-source free software capable of simulating circuits<p>(though ngspice has had some licensing issues in the past i think those are fixed now)<p>you can get spice models for just about any part on the market and use them in ngspice, wr-spice, or the original berkeley spice, though not falstad&#x27;s circuit.js or omedit<p>relevant to this week&#x27;s tantalizing superconductor news, wr-spice is the only one with a decent josephson junction model

Not open source but Free: Micro-Cap 12 <a href="https:&#x2F;&#x2F;web.archive.org&#x2F;web&#x2F;20230219052113&#x2F;http:&#x2F;&#x2F;www.spectrum-soft.com&#x2F;index.shtm" rel="nofollow noreferrer">https:&#x2F;&#x2F;web.archive.org&#x2F;web&#x2F;20230219052113&#x2F;http:&#x2F;&#x2F;www.spectr...</a>