I bought this in New York on one of those days when you sit on a park bench and your sweat leaves an imprint when you get up. My friend Ryan and I limped around in the heat but managed a both a gander and purchase at No Relation Vintage in the East Village.
I really like it because even though it's long and gown like, it's made of a light summer cotton that can easily be worn casually. It's handmade and I would say it's from the 1970's.
Coincidentally, Ryan just sent me a photo of the pub that we spent the rest of that afternoon in; here it is in the 1940's: