Tuning forks have been used for around 300 years, originally for tuning musical instruments. They are now used for many other purposes, including:
Physics
Tuning forks are one of the most precise instruments in physics. They can be used to test the vibration of objects, such as a physician striking the fork and placing it on different parts of a patient's body.
Medicine
Tuning forks are used to diagnose hearing disorders and bone fractures.
Sound therapy
Tuning forks vibrate at a set frequency after being struck on the heel of the hand. They can be used to help with chronic stress, chronic pain, tiredness, headaches, insomnia, and more.