I thought it was a zigzag attachment but wanted to read what had been posted already!

Hooray for llg930!!
I followed her link and lo and behold, there it was, about half way down the page.

"llg930 writes: hi ok i found your mystery foot here is
the link and description:

http://www.raindropkites.co.uk/sewingmachines/bigatts.html"

Way to go!!

Rufflers have more working parts and although it might have been used as a buttonholer (and states that on the referenced web page) I believe the primary use is to overcast. Indeed, the one above it is shown on that page as creating a three stitch zigzag, typically what is used today to attach elastic and form a flexible seam (the extra "toe" on that one might have been a guide for the elastic!)