So I was on the prowl this early morning looking for a tool to rescue, and this followed me home.
It is a 12" Bigelow & Dowse backsaw. I didn't know much about it, but I know a bit more now. Bigelow & Dowse were in business in Boston starting in 1884. I don't know when they closed their doors. The saw looks late 19th, or early 20th century.
I cleaned it up, a quick sharpening with an XXS file, some BLO and wax, and she's ready for another 100 years.
I didn't take any before photos, but here are the after:
the cut edge in pine: