$3.99 from Sonzea
As long as you have your iPhone, you’ll never play out of key again with Stay In Tune. A powerful and flexible instrument tuner for the iPhone, Stay In Tune can tune all types of stringed and wind instruments using iPhone’s built-in microphone. Featuring a large and easy-to-see display, this little application is a must for any musician.
Stay In Tune version 1.2 can tune a broad range of instruments thanks to its versatile Chromatic tuning mode. It also supports tuning modes for the Guitar, Drop-D tuned Guitar, Banjo, Violin, Viola, Cello, Mandolin, and Ukulele.
Stay In Tune allows you to tune visually using its highly accurate tuning engine or by ear with built-in reference notes. You can also fine-tune your instrument to off-pitch tunings using the calibration feature.