Best Free Circuit Simulators 2026: 6 Options Compared

Circuit simulators fall into two camps: SPICE engines that solve real analog circuits, and teaching tools that animate what is happening. LTspice and ngspice sit in the first camp. LTspice is free from Analog Devices for Windows and macOS and is the usual choice for power supplies and analog stages, though it is freeware rather than open source. ngspice is the open source engine many other programs embed. Qucs-S gives ngspice and other engines a schematic editor, and KiCad's schematic editor includes a simulator for people already drawing their boards there. Falstad's circuit simulator runs in a browser and animates current and voltage as you build, which makes it better for learning than for verifying a design. Logisim-evolution is separate: it simulates digital logic, not analog parts. Choose by question. If you are checking whether a power stage will oscillate, use LTspice or ngspice with real component models. If you are explaining how a filter works to a class, open Falstad's simulator. The usual trade-off is model availability: free simulators ship with generic parts, and the exact vendor model for a chip often has to be downloaded and checked by hand. A simulation is only as good as the model behind it.

LTspice

Free SPICE simulator from Analog Devices, with Windows and macOS builds listed on its page. Freeware rather than open source, and best with Analog Devices parts.

Price: Free (Page calls it a fast, free SPICE simulator; no usage limits stated) (LTspice pricing, checked 2026-10-24).

Platforms and license: Windows, macOS. Proprietary freeware.

Best for: Analog and power circuits.

Falstad Circuit Simulator (CircuitJS)

Falstad's simulator runs in the browser and animates current as you build. Excellent for teaching; not meant for verifying a production design.

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).

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

Best for: Learning and demonstrations.

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

ngspice

Open-source SPICE engine, free to download. Command-line and library oriented, so most people use it through a schematic front end.

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).

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

Best for: Embedding SPICE in other tools.

Qucs-S

Free GPL-2.0 schematic front end for ngspice, Xyce and other engines on Linux, Windows and macOS. Simpler than a full EDA suite.

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).

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

Best for: Drawing and simulating in one app.

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

KiCad

Free GPL-3.0 PCB suite whose schematic editor includes a simulator, per the KiCad documentation. Simulation is an add-on to the board design workflow.

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).

Best for: Simulating while designing a board.

Compare: KiCad alternatives

Logisim-evolution

Free GPL-3.0 designer for digital logic circuits with installers for Windows, macOS and Linux. Digital only; it does not solve analog circuits.

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

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

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

Best for: Digital logic 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 test analog or power circuits on Windows or macOS: LTspice
• You need a circuit simulator for a classroom demo: Falstad Circuit Simulator (CircuitJS)
• You already design boards in KiCad: KiCad
• You study logic gates and CPUs: Logisim-evolution
• You want a free GUI around ngspice: Qucs-S