This is similar to bel / custard apple, but smaller and not so sweet version.
To check whether they are ripe, you should drop them on the floor or kitchen counter from a height of 2-3 feet, if they do not bounce, they are ripe and will break easily (though not from dropping)
Ingredients for wood apple chutney-
2 wood apples
1 tsp chopped garlic
2 green chillies chopped
2 tbsps coriander chopped
1 tsp panch phoran
Salt to taste
1 tsp Turmeric powder
Oil for seasoning (1 tsp)
Wash and break the wood apple, scoop out the pulp. Soak in a bit of water in a medium bowl for 15-20 mins. Mash using a potato masher.
You can also grind the pulp if you like.
Heat oil in a wok. Add panch phoran, coriander, chillies, garlic. Fry till the garlic is cooked. Add turmeric and cook for a few secs. Add the wood apples paste, add jaggery, salt and cook for a couple of mins. Let cool a bit before serving.