Rhino.Inside is a new technology that enables Rhino software to be embedded in other 64-bit Windows applications. Rhino Inside Revit - Rhino in Revit - is a platform that runs on this technology and offers an unprecedented level of integration between Rhino and Revit.
Technically speaking, Rhino.Inside runs like any Revit plugin by embedding Rhino and its plugins (eg Grasshopper) in Revit's memory. Grasshopper provides Revit interaction with a number of new components that use the script, and provides access to the API (Application Programming Interfaces) of both software.
On the practical side, Rhino.Inside.Revit opens up Grasshopper's rich ecosystem to the Revit environment, as a bridge connecting Rhino's free-form modeling capabilities and the BIM world with a set of tools, offering a completely new concept of design and possibilities.