MATLAB - A high-level language and interactive environment for numerical computation, visualization, and programming
LTspice - LTspice® is a high performance SPICE simulation software, schematic capture and waveform viewer with enhancements and models for easing the simulation of analog circuits.
GNU Octave - GNU Octave is a programming language for scientific computing.
Circuit Simulator - Animated electronic circuit simulator using ideal components to visualize voltage and current.
Wolfram Mathematica - Mathematica has characterized the cutting edge in specialized processing—and gave the chief calculation environment to a large number of pioneers, instructors, understudies, and others around the globe.
Solve Elec - Solve Elec is a free educational program to draw and analyze electrical circuits.