Amalaki (Sanskrit) / amla (Hindi) / nellikai (Tamil) / Indian gooseberry is said to be good for acidity in Ayurveda. The fruit part of the plant, phyllanthus emblica, IIRC. Very widely used in India in different forms for many ailments. There is amla eaten raw, amla juice, amla murabba (a sort of sweet dried or wet candy), amla in honey (just had it today), in triphala, etc. Rich in Vitamin C and has many benefits.

I use it.

Triphala, another Ayurvedic remedy, is said to be a general-purpose cleanser / gut detoxifier/ digestive tonic. Very commonly prescribed by Ayurvedic doctors.