KiCad - A Cross Platform and Open Source Electronics Design Automation Suite
Emulino - an emulator for the Arduino platform by Greg Hewgill
Proteus PCB design - Proteus PCB design combines the schematic capture and ARES PCB layout programs to provide a...
SimulAVR - The SimulAVR program is a simulator for the Atmel AVR family of microcontrollers.
Altium Designer - PCB Design Software
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.