Circuit Simulation
SPICE-family analog/mixed-signal simulators, plus interactive teaching simulators.
Where you verify a circuit before laying it out. For schematic capture proper see PCB / EDA Suites; for code-described circuits see Programmatic CAD.
SPICE engines (the core)
- ★ ngspice — the maintained open-source SPICE3f5 successor. GPL. Engine inside KiCad's simulator, GNU Octave's circuit toolbox, and many GUIs. The default FOSS SPICE engine in 2026.
- ★ LTspice XVII / LTspice 24 — Analog Devices' free closed-source SPICE. Windows-native (runs fine via Wine / CrossOver on Mac/Linux). Renowned solver, huge SMPS / power-electronics community, Analog Devices' part models. Free as in beer; not open source.
- Xyce — Sandia's parallel SPICE. Open source, scales to very large netlists. Niche unless you genuinely need parallelism.
- Qucs-S — Qt frontend that can drive ngspice, Xyce, or QucsLib's own engine. Active in 2025–2026.
- Qucs (classic) — original Qucs; mostly superseded by Qucs-S.
- NGSPICE-OpenVAF — ngspice with OpenVAF Verilog-A compiler; lets you use modern compact transistor models (BSIM, etc.) in FOSS flows.
GUI frontends
- ★ KiCad's bundled simulator — built on ngspice; tightly integrated with the schematic editor since v7+. The path of least resistance if you're already in KiCad.
- Qucs-S — see above; capable schematic + waveform viewer.
- Micro-Cap 12 — formerly commercial, fully free since 2019; Windows-only. Excellent SMPS analysis. Frozen in time but still very usable.
- TINA-TI (Texas Instruments) — free, Windows-only, with TI's part models built in.
- PSpice for TI — TI's free-for-TI-parts version of Cadence PSpice.
- SIMetrix Intro — free entry tier of SIMetrix; limited node count.
Browser / interactive teaching simulators
- ★ Falstad / CircuitJS — beloved interactive analog simulator in the browser; great for teaching. MIT-licensed.
- EveryCircuit — slicker animated interactive simulator; freemium (free tier limited).
- PartSim — browser SPICE; Aspen Labs.
- CircuitLab — browser EDA + simulator; paid.
- Tinkercad Circuits — Autodesk's drag-and-drop simulator; great for kids and Arduino prototyping.
- Wokwi — Arduino / ESP32 / Raspberry Pi Pico simulator with a real-time virtual scope, logic analyzer, and Wi-Fi simulation. Free tier; paid for private projects. The default for embedded prototyping in the browser in 2026.
Digital / mixed-signal / HDL
- Verilator — fast Verilog simulator (compiles to C++). The default open-source HDL sim.
- Icarus Verilog — older event-driven Verilog sim.
- GHDL — VHDL simulator.
- CXXRTL — Yosys' built-in cycle sim.
- GTKWave / Surfer — open-source waveform viewers (Surfer is the modern, actively-developed one).
- Digital — JAR-based logic-circuit teaching simulator; great for university courses.
Specialty / RF / EM
- OpenEMS — FDTD electromagnetic simulator; free.
- Sonnet Lite — free RF planar EM, node-limited.
- FEMM — 2D magnetics / electrostatics / heat; free, Windows.
- Elmer FEM — open-source multiphysics; includes EM solvers.
Pick this if…
- Default FOSS analog SPICE in 2026: ngspice (often via KiCad).
- Best free SMPS / power-electronics simulator: LTspice.
- Need parallel scaling on huge netlists: Xyce.
- Teaching / blogging interactively: Falstad / CircuitJS.
- Embedded MCU prototyping in-browser: Wokwi.
- HDL (Verilog/VHDL) simulation: Verilator + Surfer.
- Quick mixed-signal with TI parts: TINA-TI.