Double Boiler
Two pots, one which sits on top of the other. The bottom pot contain boiling water, the top pot contains whatever is being cooked. This tool is useful for making delicate sauces or melting chocolate or any other occasion when you don't want to have direct heat on the food which is being cooked.

You can improvise a double boiler by placing the items to be cooked in ametal bowl, which is placed over a pot of boiling water.

double boiler