Pitcha

It uses the McLeod Pitch Method to estimate the fundamental frequency of the raw sound data that is being recorded by the microphone.

It works with all recorded sound, such as human voices, whistling, and musical instruments - try it out.

Limitations:

Due to the nature of smartphone microphones, the frequency range isn't very large. It has trouble with frequencies lower than the low E on a guitar. I have not found the high limit yet.

Usage:

Place phone near audio source and make sure the sound is sustained and clear. For example, with a guitar, pick the string hard, and let it ring for ~2 seconds.