A free program for Android, by Guitar Tuner Apps.

The Guitar Tuner – Easy Tune app is easy to use, even for beginners. You can tune any instrument using your phone’s microphone, with no need for an external device.

The app displays the notes in real-time as you tune the instrument. It also shows the frequency of the note, allowing you to easily find the pitch. The app can also be used as a metronome, with an option to set the tempo. It also includes a database of chords, allowing you to easily find the chords and play the right note.