These are a wild melon called "kachri" or "sane" found in various parts of South Asia. You'll often see these for sale at markets in both rural villages and urban markets in Northern India. They range in color from green to yellow and can be as nearly as big as a football to about the size of a walnut. As they are wild and never cultivated you'll often see kachri vines volunteering along roadsides, amidst crops, and in jungle thickets throughout India.
This rather blurry photo shows how they look when ready to be picked, the vine withers and the small melons can be green to yellowish brown. The flesh inside is watery and seedy like a cucumber and can range from pale green to yellow. When green kachri can have a bitter astringent taste but when ripened they turn yellow and have a definite melon flavor that's rather tart.
I've seen fresh slices of kachri being sold at markets in Delhi for snacking as well as children in the countryside in Uttar Pradesh nibbling on them. Kachri are quite popular in Rajasthan where the harsh desert climate makes growing most vegetables impossible. Rajasthanis make several chutneys and vegetable curries out of kachri.
Here you can see how tiny the melons can be. Since they are a feral and foraged (or "wildcrafted" as the hipsters say) fruit their size depends primarily in the conditions in which they grew. South Asian cultures have a lot of these foraged plants in their cuisines that you don't often see nor hear about in cookbooks.
Kachri are also sun dried for later use in India. They are then ground to powder for use in chutneys or as a meat tenderizer. Kachri powder is also used as a souring agent much like amchur or dried mango powder. It is advised to buy dried kachri whole and grind them yourself as flavor is said to dissipate after grinding. There are commercially available brands of kachri powder available though.
Guess where else you can find kachri powder? Yes, indeed! It's souring my favorite chat masala by the brand Catch!
Catch brand Magic Chat Masala ingredients : Salt, Dry Mango, Kachri, Black Salt, Cumin, Bishop's Weed, Mint, Long Pepper, Sugar, Black Pepper, Tartaric Acid, Big Cardamom, Red Chilli, Clove, Cinnamon, Coriander, Nausadar, Asafoetida
That's what I love about these Catch brand masalas. They have these really unique blends featuring traditional spices that have become a bit obscure in modern times. This really stands out in the complex flavors of their spice blends. (If you are wondering what the ingredient "nausadar" is it's ammonium chloride. The same ammonium chloride that's used in Scandinavian salty licorice.)