CentTuner is a responsive and accurate chromatic tuner. It uses the iPhone's microphone for determining the pitch. The detected pitch is given straight away, as the closest note, and a meter tells you if the tone is in tune, or it is too flat or sharp.
The Best Features

RESPONSIVE

Responsive and optimized - several results each second.

ACCURATE

Accurate within cents of the tone.

CLEAN INTERFACE

Simple and clean user interface makes it easy to use.

FREE

All this for free.


Background is a modified version of a photo by Feliciano GuimarĂ£es from GuimarĂ£es, Portugal (Electric guitar Uploaded by tm) [CC BY 2.0], via Wikimedia Commons