Alternatives to LTspice
A free SPICE circuit simulator with schematic capture and a waveform viewer, from Analog Devices. The listings below can replace it for an important use case. Each note says what changes if you switch.
The original
LTspice
A free SPICE circuit simulator with schematic capture and a waveform viewer, from Analog Devices.
Replacements
Listings that take over the same core job as LTspice.
ngspice
An open-source SPICE simulator for analog, digital and mixed-signal electronic circuits described as netlists.
ngspice is open source and handles analog, digital and mixed-signal simulation from netlists, accepting LTSPICE models, but it has no built-in schematic entry.
Qucs-S
An open-source circuit simulator interface that drives SPICE engines such as Ngspice.
Qucs-S is an open-source graphical front end for SPICE engines such as Ngspice, running on Windows, macOS and Linux, while LTspice is Windows only.
Proteus Design Suite
Electronics design software combining schematic capture, circuit and microcontroller simulation, and PCB layout.
Proteus Design Suite adds microcontroller firmware simulation and PCB layout to circuit simulation, but it needs a commercial licence with pricing not listed on its homepage.
OrCAD X
Cadence's commercial PCB design suite for schematic capture, simulation and board layout.
OrCAD X is Cadence's commercial Windows suite combining schematic, SPICE and mixed-signal analysis in higher editions, plus PCB layout, with paid licences.
Similar software
Related functionality, not a direct replacement.
KiCad
A full electronics design suite: draw the schematic, lay out the board, view it in 3D, send it to a fab.
Tinkercad
Create simple 3D designs and explore electronic circuits in a browser.
EasyEDA
Design electronic schematics and printed circuit boards in a browser.
Altium Designer
Professional PCB design suite covering schematics, layout, and simulation.
CircuitMaker
Free schematic and PCB design software from Altium with a community component library.
Fritzing
Document electronics projects with breadboard, schematic and PCB views.
