These models were originally manufactured in Japan by Kato (then known as Sekisui Kinzoku). Production was later relocated to Chicago.
Steel-sided / fishbelly-sided gondolas like these date back to at least the late 1930s. I'm told that the fishbelly-sides were introduced to add more strength to the center of the car. For the most part, these cars are actually 52' or 53' in real life (as opposed to 50'). The reason N scale has so many 50' gondolas is simply because it allowed manufacturers to save money by recycling the 50' underframes from their box cars.
Open gondolas like these are used to transport just about anything that can be loaded using an overhead crane - coal, garbage, cable, railroad ties, iron, logs, piling, pipe poles, posts, rip rap, rock, rods, scrap metal, steel, tin, tubes, wire (and on and on).