Elizabeth Bustamante @ snapeda.com lists the top 10 crystal oscillators used today. She writes:
A crystal oscillator is an electronic circuit that generates an electrical signal with a very precise frequency. To achieve this, it uses the mechanical resonance of a vibrating crystal made of piezoelectric material.
The first crystal oscillator was invented in the late 1920s by Walter Guyton Cady who was interested in submarine detection with ultrasonic waves. He suggested that a piezoelectric resonator could be used as a frequency reference, a coupling device between circuits, or a filter.
The top 10 crystal oscillators from SnapEDA – [Link]