Skyangel - it's a very early buttonholer. SteveH had posted pictures of his, and I remembered seeing this one on Ebay and wondering what it was.
http://www.quiltingboard.com/vintage...r-t228034.html
I was the only bidder so I figure no one else realized what it was, or maybe no one was in the market that day. Seller had no clue - just listed it as Puzzle box with attachments. I paid $36 including shipping.
More often someone else knows what they are looking at. Recently there was a mixed lot that contained a single thread embroidery attachment - the lot when for over $100. Then before that was a lot that had the stripper part for a fagoter set, and that also went for $100. In both cases, the rest of the items were worth maybe $20 for all of them together. And for both, the seller had no clue that in their pile of run-of-the-mill attachments, they had one very rare item.