In my attempt to do away with my dependency on plastic packets of refillable hand soap and liquid detergent, I came to realize one thing: there is almost always a natural substitute for everything we have developed.
My research led me to soapberries.
Indigenous to the Himalayas are Sapindus, a plant that's a member of the lychee family. These shrubs produce berries that have traditionally been pulped to make soap. The use of its nuts (drupes, they're called) dates back to ancient Asia and America.
Soaking the soapberries in hot water releases saponin, a detergent-like compound. The liquid is like a mild soap, with a lightly tart scent. I've added my own essential oils to it, used it for washing plates and laundry. While it's not as effective as detergents laden with chemicals, it definitely does the trick for things that need a gentle wash.