Project Nucleus integrates the Nucleus simulation engine from Autodesk® Maya® into Autodesk® Revit® Architecture and Project Vasari. It allows designers to experiment with "form-finding" in the conceptual design phase by simulating forces directly in Revit Architecture and Project Vasari. (The latest technology preview of Project Vasari includes the Project Nucleus functionality.)
Project Nucleus can simulate a wide range of physical phenomena in real time, like wind, gravity, constraints, and collisions. These forces can help architects generate free-form shapes, many of which would be impossible to model by hand.
More information here.