What crop is this?
This is a luffa gourd (Luffa aegyptiaca). A similar species (Luffa acutangula) is sometimes also called Chinese okra because of its okra-like shape and pronounced ribbing of its fruit. Both are members of the cucurbit family. Luffas may be harvested for eating while still tender, though the species pictured is very fibrous and is used as a sponge or dishcloth. Plants are vigorous vines and are grown just like melons and squash. They are most productive when trained on a trellis and can produce 10 to 20 fruit per plant. Fruits are elongated, cylindrical and may be more than a foot long. Read more about luffa gourds here (referred to here as Chinese okra).
For more information on growing and using the fibrous luffa gourd (Luffa aegyptiaca), see HGIC Growing Luffa and HGIC Making Luffa Soap.