Welcome to the IFC Export for Revit Sourceforge project! This project contains the .NET code and DLL used by the Revit 2012 and 2013 families of products that support IFC export. The open source version can override the version that comes standard with shipped Revit.
The newest version is for R2013, and is based on R2013.
The base version of the R2012 code is based on R2012 UR1. The latest R2012 code is based on R2012 UR2. This code is directly usable in R2013 - any new customization projects should use the R2013 code instead of the R2012 code, unless it is specifically intended to work with R2012 only.
Feel free to ask any questions in the Discussion area, or download and play with the code yourself.