This is the .NET code used by the Revit 2015 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 2013-2015 contain both IFC export and IFC export UI overrides, which contains options not available in the regular UI, such as ifcXML and ifcZIP support. The Revit 2014 and 2015 versions also work for Revit LT 2014 and 2015, respectively.
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.