Anyone know what this was used for?

My wife's mom collected interesting antiques. She had a nice (small) assortment of different woodworking tools. This one device was among them. Neither she nor I know what it could be used for. I have found lots of pictures of Keen Kutter tools on eBay and on antique sites. But none like this.
Made by Keen Kutter so it was clearly meant to cut something. But what?
Thank you!