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.
VBB electronic circuit components are modeled at the function block level and are wired together to create a real-time interactive circuit simulation representing the whole embedded application.
VBB does not use SPICE. SPICE is better suited to subcircuit designs whereas VBB is concerned with merging multiple subcircuits treating each subcircuit as a self contained function block.