Chameleon is a plugin for both Grasshopper and Revit with a focus on interoperability, simulation, and efficient practice workflows. Chameleon’s main advantage is its ability to facilitate easy transfer of geometric data between Grasshopper and Autodesk Revit, but also includes other valuable tools to make life easier, both in Grasshopper and Revit.
Chameleon is currently compatible with Revit Architecture 2012, 2013 and Grasshopper 0.8.0066.
There is a Chameleon Forum on his Revit City site as well as Chameleon Group at

This latest version includes upgraded the functionality of the Curtain Grid management tools for Revit users. These tools now allow control of curtain panels in addition to the grids and mullions. There is also a preview to show the results of changes before accepting.