It can be used to perform circuit simulations, and now includes a full, working virtual Arduino. Looks to be Windows only.
VirtualBreadboard is an easy to use simulation and modelling tool that can be used in place of a real breadboard for quickly performing experiments and testing out electronic and microcontroller powered 'embedded' applications. Since 1999 VirtualBreadboard has been a favourite with universities and enthusiasts from all around the world.
VirtualBreadboard (VBB) is for designing and testing embedded software in high-level interactive circuit simulations and rapidly prototyping hardware from those designs. Compared to other simulators many people find the high level approach taken VBB easier to use and much faster to model and test out new ideas and circuit variations.
http://blog.makezine.com/archive/2010/0 … duino.html
Thought I would share this for anyone using Arduinos to play around with. Might help cut back on the buying/acquiring of wrong parts if one gets to virtually play test them.