Xyce - Xyce is an open source, SPICE-compatible, high-performance analog circuit simulator, capable of solving extremely large circuit problems by supporting large-scale parallel computing platforms.
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
simavr - a lean and mean Atmel AVR simulator for linux
Oregano - oregano - An electrical engineering tool for GNOME
SimulAVR - The SimulAVR program is a simulator for the Atmel AVR family of microcontrollers.
Circuit Simulator - Animated electronic circuit simulator using ideal components to visualize voltage and current.