With microcontrollers costing less than the 74HC14 itself, why bother with discrete oscillators? Because the 74HC14 teaches timing at the atomic level. The calculator transforms abstract math into tangible results — turn a knob (potentiometer) and hear the speaker pitch change, see the LED blink rate shift.
The 74HC14 is a popular hex inverter Schmitt trigger IC, and it's commonly used to build simple oscillators. Here's a full story on how to calculate the oscillator frequency using a 74HC14: 74hc14 oscillator calculator full