Which fruit has a shell so hard that it is sometimes opened with a machete?

Coconut

The coconut is well known for its extremely hard outer shell, called a drupe, which often requires the use of a sharp object like a machete to open. In addition to its refreshing water and tasty flesh, the coconut is used in a variety of ways in tropical cultures - from making coconut milk to coconut oil, and even in construction and crafts. The fibers of the coconut shell, known as coir, are processed into ropes and mats. This versatility makes the coconut a vital resource in tropical economies.