Is it 2007? I remember seeing it much earlier - like 2001-2002 or so. Maybe SwingSet2 was the follow-up to some SwingSet1 that came earlier, and which contained a lot of the same stuff?
Yes, there was an earlier SwingSet, but someone told me that even SwingSet2 was earlier than 2007 (I went by the first copyright year on the source code).
Edit: close enough, 2007