Solve Elec - Solve Elec is a free educational program to draw and analyze electrical circuits.
MATLAB - A high-level language and interactive environment for numerical computation, visualization, and programming
simavr - a lean and mean Atmel AVR simulator for linux
GNU Octave - GNU Octave is a programming language for scientific computing.
Emulino - an emulator for the Arduino platform by Greg Hewgill
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.