These ready-to-run cars feature prepainted and lettered, injection-molded styrene bodies. Models include free-rolling Delrin(R) trucks with contoured axles, truck-mounted Magne-Matic(R) couplers and diecast metal underframes. Open hopper cars feature opening hopper doors.
As pictured above, these models are available with Flat Ends, Peaked Ends or Notched Peak Ends (the latter being popular with a number of eastern coal railroads). Some of these cars are available with coal loads. In addition to being sold separately, they're also available in 4-unit "Runner Packs".
I don't know what specific prototype(s) these models might be based on (if any), but rib-sided hoppers of this general type date back to at least the late 1930s. Cars of this type were generally used in coal service. The unique design (with the ribs on the outside of the car) resulted in less corrosion and damage to said support elements.