Kumquat

Cumquats or kumquats are a group of small fruit-bearing trees in the flowering plant family Rutaceae, either forming the genus Fortunella, or placed within Citrus sensu lato. The edible fruit closely resembles that of the orange (Citrus sinensis), but it is much smaller and ovular, being approximately the size and shape of an olive.
Uses
Koum Quat liqueurs from Corfu, Greece

Kumquats are often eaten raw. As the rind is sweet and the juicy centre is sour, the raw fruit is usually consumed either whole—to savour the contrast—or only the rind is eaten. The fruit is considered ripe when it reaches a yellowish-orange stage and has just shed the last tint of green.

Culinary uses include candying and kumquat preserves, marmalade, and jelly. Kumquats can also be sliced and added to salads. In recent years kumquats have gained popularity as a garnish for cocktail beverages, including the martini as a replacement for the more familiar olive. A kumquat liqueur mixes the fruit with vodka or other clear spirit. Kumquats are also being used by chefs to create a niche for their desserts and are common in European countries.
Potted kumquat trees at a kumquat liqueur distillery in Corfu.

The Cantonese often preserve kumquats in salt or sugar. A batch of the fruit is buried in dry salt inside a glass jar. Over time, all the juice from the fruit is diffused into the salt. The fruit in the jar becomes shrunken, wrinkled, and dark brown in colour, and the salt combines with the juice to become a dark brown brine. A few salted kumquats with a few teaspoons of the brine/juice may be mixed with hot water to make a remedy for sore throats.[citation needed] A jar of such preserved kumquats can last several years and still keep its taste.[citation needed]

In the Philippines and Taiwan, kumquats are a popular addition to green tea and black tea, either hot or iced.

In Vietnam, kumquat bonsai trees (round kumquat plant) are used as a decoration for the Tết (Lunar New Year) holiday. Kumquat fruits are also boiled or dried to make a candied snack called mứt quất.

Variants of the kumquat are grown specially in India. (source from wiki)

Author's Input:
My mom has five of these fruit trees planted in her back yard and it's a treat to see the tree when it's covered with little tiny bright orange fruits.  You can eat these fresh off the tree.  When we have a cough, this little fruit was our friend.  My mom usually drieds some of the fruits and stores it for future use in teas or just eaten like prunes.  Personally, I don't like the prune way of eating it but I do like making a soft drink with it.  I would add about two of these salted kumquats in a cup of boiling water with rock sugar.