This is the .NET code used by the Revit 2015-2017 family of products to support IFC, and the Revit 2012-2014 families of products to support IFC export. The open source version can override the version that comes standard with shipped Revit. Revit 2013-2017 contain both IFC export and IFC export UI overrides, which contain options not available in the regular UI, such as ifcXML and ifcZIP support. The Revit 2014-2017 versions also work for Revit LT 2014-2017, respectively.
This project is really paving the way for a collaborative construction industry, the developers are always on hand to deal with any bugs, wishes or queries.
Brilliant to get frequent updates between releases for IFC exports, and great possibility to intereact directly with the developers through the discussion forum. Still, there's a bit of a way to go before things work reliably... Also wish for a better UI to get control over what comes out.