1) Place the peaches, plums or nectarines that you wish to ripen in a single layer in a paper bag. Add a ripe banana to the bag. Roll the top loosely and leave the bag on the counter. Check the fruit each day to see if it is ready.
2) Arrange larger quantities of fruit in a single layer in a shallow cardboard box so that none of the fruit is touching. Cover lightly with newspaper and place in a dark cupboard. Check the fruit daily.
3) Place the peaches, plums and nectarines on a linen or cotton cloth and drape another cloth over the fruit. Check daily until the fruit is soft. Some people think this method is the least likely to promote rotting, though it can take longer than the paper bag method.