PICsim

PIC microcontroller simulator

Emulino

an emulator for the Arduino platform by Greg Hewgill

Oregano

oregano - An electrical engineering tool for GNOME

Proteus

Proteus - Proteus is a great electrical suite for circuit simulation purposes. You can simulate a single processor or multiple ones at the same time. The application is a great alternative for Virtual System Modelling.

SimulAVR

The SimulAVR program is a simulator for the Atmel AVR family of microcontrollers.

simavr