Project Vasari technology preview Is Now Available
Project Vasari is a design tool with analysis capabilities available via the cloud. Project Vasari is compatible with Revit in that files created by Project Vasari can be opened using Revit 2011, and Revit files can be opened by Project Vasari. There are some limitations in that, as a conceptual modeler, Project Vasari does not support some features (e.g., detailed model elements such as walls, windows, doors, etc.) The thinking is that you would start with Project Vasari and then continue with Revit 2011 to make more detailed models - not the other way around.
In a nutshell… Project Vasari it's basically Revit for people who don't need all of Revit.