Fritzing is an ultimate tool for document the Arduino-based prototype and create a PCB layout for manufacturing. Similar to Arduino, Fritzing is also an open-source project. There are tons of electrical components library predefined for you or you can create some yourself. It supports breadboard, schematic and PCB views.
Fritzing is a powerful Arduino prototyping software but it is not a Arduino board software simulator.
Latest version of Fritzing can be downloaded from Fritzing Official Website.