Hoffman’s was a pre-war manufacturer of OO gauge freight car kits in Philadelphia. Their kits included painted and lettered card sides, wood bodies, and cast details, including sprung Bettendorf trucks. The line included:

Box car, RDG, DL&W
Flat car, RDG
Gondola, RDG
Reefer, wood, MDT, ARLX, FGEX
Caboose, eight wheel

These models are completely unique and not common at all. A reefer is above, and the first Hoffman’s advertisement from 1938 is below.

UPDATE: To see more on Hoffman’s please check my book on American OO.