Soap berries, or soap nuts, contain saponin, a natural detergent that is gentle on those who need an alternative to harsh chemicals.
Use a bag of 4-5 deseeded berries and place in a washer. Wash as per normal, remove before rinsing. Each bag can be used 3-4 times (or more) until there are no more suds.
You can use it as a dishwashing liquid, an all-purpose cleaning agent, or even shampoo!