I'm not sure papaya can really be considered a herb, but it is a plant product and does have some health benifits.  The main use of papaya, other than food, is for upset stomach caused by excess acid.  People who frequently take over-the-counter antacids can sometimes get better results by eating papaya.  Taking antacids frequently sometimes causes a rebound effect where the body starts producing even more acid, requireing you to take even more antacid.  Papaya does not cause this rebound effect.  When fresh papaya is not available, you can get papaya juice and tablets.
    In addition to being a digestive aid, papaya has cancer-fighting properties.  It's high in vitamins including C, E, A and K.  The Center for Science in the Public Interest rated it number five on their list of most nutritious fruits.  It can thin the blood and prevent clotting.  It can fight intestinal worms and other internal parasites.  Some experiments with mice show it may be able to reverse some types of loss of fertility.  It can also benefit gallbladder problems, pancreatic inflamations, ulcers and varacose veins.