Free analog electronic circuit simulators

• Electric VLSI Design System
  Electric (software)
  The Electric VLSI Design System is an EDA tool written by Steven M. Rubin.Electric is used to draw schematics and to do integrated circuit layout.It can also handle hardware description languages such as VHDL and Verilog....
  
  , used to draw schematics and lay out integrated circuits.
• gpsim
  Gpsim
  gpsim is a full system simulator for Microchip PIC microcontrollers.It is distributed under the GNU General Public License.From their website:...
  
  
• LTspice Windows and Linux under Wine
• TINA-TI Free SPICE variant that includes many TI component libraries
• SimOne
• SapWin
  SapWin
  SAPWIN is proprietary a symbolic circuit simulator written in C++ for the Windows environment. Unlike more common numerical circuit simulators , SAPWIN can generate analytical Laplace domain expressions for arbitrary network functions of linear analog circuits...
  
  
• SPICE
  SPICE
  SPICE is a general-purpose, open source analog electronic circuit simulator.It is a powerful program that is used in integrated circuit and board-level design to check the integrity of circuit designs and to predict circuit behavior.- Introduction :Unlike board-level designs composed of discrete...
  
   and variants
• Oregano (software)
  Oregano (software)
  Oregano is a graphical software application for schematic capture and simulation of electrical circuits. The actual simulation is performed by the ngspice or Gnucap engines. It is similar to gEDA and KTechlab. It makes use of GNOME technology and is meant to run on open source Unix environments...
  
  
• PSIM (unlimited time demo)

Free digital electronic circuit simulators

• CPU Sim
  CPU Sim
  CPU Sim is a software development environment for the simulation of simple computers. It was developed by Dale Skrien to help students understand computer architectures. With this application the user is able to simulate new or existing simple CPUs. Users can create new virtual CPUs with custom...
  
  
• KTechLab
  KTechLab
  KTechlab is an Open Source IDE for electronic and PIC microcontroller circuit design and simulation. Featuring an extensive circuit designer with autoroutingand simulation of all common electronic components and logic elements....
  
  
• Logisim
  Logisim
  Logisim is a logic simulator which permits circuits to be designed and simulated using a graphical user interface. Released under the GNU Public License, Logisim is free software designed to run under the Microsoft Windows, Mac OS X, and Linux platforms. Its code is entirely in Java using the Swing...
  
  
• Chipmunk-diglog
• Paul Falstad's online java circuit simulator http://www.falstad.com/circuit
• TkGate

Free mixed-signal (analog & digital) electronic circuit simulators

• GNU Circuit Analysis Package
  GNU Circuit Analysis Package
  Gnucap is a general purpose circuit simulator started by Albert Davis in 1993. The latest stable version is 0.35 from 2006. The latest development version is from December 2009 and is quite usable....
  
   (Gnucap)
• Micro-Cap
  Micro-Cap
  Micro-Cap. is a SPICE compatible analog/digital circuit simulator with an integrated schematic editor that provides an interactive sketch and simulate environment for electronics engineers. It is developed by Spectrum Software and is currently at version 10....
  
  , student version free of charge
• Ngspice
  Ngspice
  Ngspice is a mixed-level/mixed-signal circuit simulator born around 1999 as a "student project" in the Electronics Engineering Department of University of Roma "La Sapienza" with the integration of BSIMSOI model into Spice3f5...
  
  
• Quite Universal Circuit Simulator
  Quite Universal Circuit Simulator
  Quite Universal Circuit Simulator is an open source electronics circuit simulator software released under GPL.It gives you the ability to set up a circuit with a graphical user interface and simulate the large-signal, small-signal and noise behaviour of the circuit...
  
  (Qucs)