The Grumman Goose is an amphibious, "flying boat" style airplane used for civilian and military usage from the 1930s to the present day. Although it is unclear whether it is still in regular passenger service, it is still flown by private owners and charter airline companies. The Grumman Goose is arguably the only pre-World War II aircraft still in regular commercial service.

Originally designed as a short-range transport for businessmen on Long Island to get to New York City, complete with bar, the big break of the Grumman Goose was World War II, where the planes ability to carry freight and people to isolated outposts, as well as its ability to patrol in maritime environments, made it an important utility aircraft for the Army Air Force, Navy and the Coast Guard. With a maximum speed of 195 miles per hour, it wasn't exactly a front line combat aircraft, but its ability to land on the ground or in the water made it indispensable in certain environments. During the 1930s and 1940s, 345 Grumman Gooses were produced, in several slightly different models. After the end of World War II, it continued in some military roles in the US, as well as in other countries. It mostly became a specialist passenger plane, and, with many modifications and alterations, was used in commercial service in locations like Alaska until 2012, when service to Akutun Island was ended. Given how many innovations were made in aviation since the 1930s, it was surprising to me that the basic airframe and design of the aircraft made it feasibly competitive with much later aircraft.
(Charter service in British Columbia that uses these planes)
(Flight training school for the Grumman Goose in Anchorage, Alaska)