Tuner-gStrings (Android) app for $1.99

Tuner gStrings provides musicians of all abilities with a customizable chromatic tuner for their Android device. Tuner gStrings lets you tune your guitar while you're on the go and works well with any stringed instrument. The tuner uses your phone's internal microphone to measure and analyze musical pitches. The app also generates reference pitches of each note if you prefer to tune to an exact tone.+