You can download special plugin for Revit Architecture called OBJ Exporter for Revit with which users can export their Revit files (such as the family .rfa files) and save them as .obj models. Works probably only for solid models.
Convert Autodesk Revit Architecture family data to 3D object graphics.
We found one software available in the database for this conversion.
Microsoft Windows software - convert rfa to obj on Windows
A Revit app for object export
Convert from rfa file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.