Tamarind has a sweet-tangy flavour that resembles the taste of tomatoes. Tamarind pulp or paste can be used as an alternative during cooking.
Curd or plain yoghurt can be used to substitute tomatoes. Curd adds a sweet flavour and tartness to the dish.
Tomatoes are often used to thicken the curry, and gram flour can be a great replacement. Gram flour works wonders for thickening a curry and adding some flavour to it.
Mango powder or amchur also has a tangy and sweet flavour like tomatoes. Mango powder is affordable and used in various dishes.
Pumpkin puree is also a great substitute for tomato puree.