I Can Drive 55
— audio speedometer
In the 80's, Sammy Hagar couldn't drive 55. If you can drive exactly 55 MPH, you'll hear him singing about it.
Drive too slow or too fast, and the music will slow down or speed up.
I've been wanting something that can limit my speed, without staring at the speedometer or going to full cruise control.
Mechanically, it would be called a governor.
Read more about governors...