Best Open-Source Circuit Simulators 2026: 6 Options Compared

Open-source circuit simulators share a common ancestor: SPICE, the program Berkeley released in the 1970s. ngspice carries the original Berkeley code under the modified BSD license and is the engine most other tools call. Xyce, from Sandia National Laboratories, is a GPL-3.0 SPICE-compatible simulator built for circuits so large that a single processor struggles. Neither has a polished schematic editor. Qucs-S supplies one, driving ngspice, Xyce and other engines from a graphical window, and KiCad's schematic editor includes a simulator tied to your board design. Falstad's CircuitJS is different in purpose: it runs in a browser and animates circuits for teaching. Logisim-evolution simulates digital logic and is the choice for course work on gates, registers and CPUs. The trade-off with open source is the same in every case: the simulator is free and capable, but the component models are your job. You will find, download and check models for the exact parts you use, and the quality varies by vendor. Pick ngspice or Xyce if you script simulations, Qucs-S or KiCad if you want a drawing window, and CircuitJS or Logisim-evolution if the goal is learning.

ngspice

Open-source SPICE engine; the COPYING file says the Berkeley code sits under the modified BSD license. Mostly used through other programs.

Price: Free (Open-source SPICE simulator; free download) (ngspice pricing, checked 2026-10-24).

Platforms and license: Desktop. Modified BSD (Berkeley SPICE base) plus other licenses; see COPYING (open source) (license source).

Project activity: 291 GitHub stars · No commits since Jun 9, 2024

Best for: Scripted analog simulation.

Xyce

GPL-3.0 SPICE-compatible simulator from Sandia, aimed at very large circuits. It has no schematic editor of its own.

Price: Free (Open source, released under the GNU GPL; source download) (Xyce pricing, checked 2026-10-24).

Platforms and license: Desktop. GPL-3.0 (open source) (license source).

Project activity: 185 GitHub stars · latest release Release-7.10.0 (Jul 21, 2025) · last commit Oct 20, 2026

Best for: Large-scale circuit problems.

Worth knowing: SPICE-compatible simulator aimed at very large circuits; command-line, no schematic editor of its own.

Qucs-S

GPL-2.0 graphical front end for ngspice, Xyce and other engines. Linux, Windows, FreeBSD and macOS are supported.

Price: Free (Free and open source) (Qucs-S pricing, checked 2026-10-24).

Platforms and license: Windows, macOS, Linux, FreeBSD. GPL-2.0 (open source) (license source).

Project activity: 1.4k GitHub stars · latest release 26.1.1 (Apr 26, 2026) · last commit Oct 25, 2026

Best for: A free schematic window for SPICE.

Worth knowing: GUI front end for Ngspice, Xyce, SpiceOpus and Qucsator, per the README.

KiCad

GPL-3.0 PCB suite with a simulator inside its schematic editor. Use it when the simulation belongs to a board you are already designing.

Price: Free (Free and open source; the about page describes no usage restrictions) (KiCad pricing, checked 2026-10-23).

Platforms and license: Windows, macOS, Linux. GPL-3.0 (open source) (license source).

Best for: Simulating alongside PCB design.

Compare: KiCad alternatives

Falstad Circuit Simulator (CircuitJS)

GPL-2.0 browser simulator that animates current and voltage. A teaching aid rather than a verification tool.

Price: Free (Free to use in the browser) (Falstad Circuit Simulator (CircuitJS) pricing, checked 2026-10-24).

Platforms and license: Web. GPL-2.0 (open source) (license source).

Project activity: 2.4k GitHub stars · last commit Oct 27, 2026

Best for: Classroom demonstrations.

Worth knowing: README describes it as a circuit simulator that runs in the browser, originally a Java applet. Animated, educational focus.

Logisim-evolution

GPL-3.0 digital logic simulator with installers for Windows, macOS and Linux. Handles digital circuits only.

Price: Free (Free and open source) (Logisim-evolution pricing, checked 2026-10-24).

Platforms and license: Windows, macOS, Linux. GPL-3.0 (open source) (license source).

Project activity: 7.8k GitHub stars · latest release v5.0.0 (Sep 12, 2026) · last commit Oct 27, 2026

Best for: Logic design coursework.

Worth knowing: Educational digital logic designer/simulator; README lists installers for Windows, macOS and Linux. Digital only, no analog SPICE.

Which one to pick

• You want to script SPICE runs: ngspice
• You want a schematic editor around a SPICE engine: Qucs-S
• You simulate circuits for a PCB you are designing: KiCad
• You teach basic electronics: Falstad Circuit Simulator (CircuitJS)
• You teach digital logic: Logisim-evolution