simavr - a lean and mean Atmel AVR simulator for linux

proteus VSM - A virtual simulation environment for electronic circuits with support of digital and analog devices.

Yenka - Yenka is a new generation of educational modelling tools from Crocodile Clips.

Pspice - OrCAD PSpice technology provides the best, high-performance circuit simulation to analyze and refine your circuits, components, and parameters before committing to layout and fabrication

PICsim - PIC microcontroller simulator

Emulino - an emulator for the Arduino platform by Greg Hewgill