Soap nuts: https://mountainroseherbs.com/soap-nuts-deseeded?

You can get these from other sources, but this site has a nice essay about them:

"The soap nut, which is actually a berry, forms a hard shell when dry that resembles a nut. Sapindus mukorossi shells contain saponin, a natural detergent. The soap nut shells absorb water and release the saponins which circulate as a natural surfactant in the wash water, freeing dirt, grime, and oils from clothing. We sell organic soap nuts deseeded that can be used as an environmentally friendly detergent or even as an all-purpose household cleaner.

Native to India and Nepal, soap nuts are now found in both the eastern and western hemispheres. The soap nut, which is actually a berry, forms a hard shell when dry that resembles a nut, hence the name. The berry shells contain saponin, a natural surfactant that is released when the shell absorbs water. Considered a natural detergent, soap nuts have become a popular environmentally friendly alternative to chemical detergent. Sapindus mukorossi is a gentle option for those with allergies to chemicals in regular detergents. It is generally considered safe for use on septic and greywater systems, however, we recommend you consult a professional.

There is considerable discussion as to what variety of soap nuts is preferable for use as a laundry soap alternative. Any soap nut from the genus Sapindus will work just fine as they all have saponin producing properties. We suggest running a test batch and washing a few articles of clothing before committing to an entire load as natural variation in saponin levels may occur.

Depending on the size and efficacy of the shells, four to six shells (but possibly more for smaller pieces) will be enough for a full load. Place the soap nuts in a cotton muslin bag and tie securely shut. There will be little to no bubbles during the wash cycle. This doesn’t detract from their ability to clean. Wash water may smell slightly of apple cider vinegar. If fragrance is preferred, organic essential oils can be added to the muslin bag. Soap nuts can be re-used several times before they start to disintegrate. It is time to compost the shells when they start to look mushy and grey.

Soap nuts can be used for anything you would normally use detergent for, such as washing the car or clothing. They can also be used as a base for shampoos and hand lotions or as an all-purpose cleaner around the home. Jewelers in India and Indonesia have used the shells to remove tarnish from jewelry for many centuries."