A tool that measures the frequency of audio input and displays it on the terminal. Requires that some nominal threshold of sound be present.

I'm currently using this to tune my violin :)

1. You need to know the frequency of the note you are tuning to.
2. Very often ends up catching the harmonic instead of the note being tuned.
3. Frequency does not remain constant (though this might be a fundamental limitation of the instrument).

1. A better interface.
2. More fine-grained a measure of frequency.
3. Tuning along with a reference frequency.