I figured farm implements but nice toIt's a piece of a sickle bar hay cutter. The moving bar containing the triangular sickles would slide back and forth on the 2 rails and the sickles would slide back and forthe through the slots. These machines were first used in horse-drawn cutters with cast iron, ground-driven wheels which were also later pulled by tractors. Then they were made for a tractor 3-point and mid-mount hitch. They're still used today.