A free program for Android, by Roland Corporation.

The BOSS Tuner app is the most convenient way to tune your Android device with the world-renowned BOSS chromatic tuner. The app is designed to allow you to use the mic in your device to tune your guitar, bass, violin, cello, trumpet, and other instruments.

In addition to supporting the standard frequencies for instruments, you can tune to the preferred frequencies for each instrument using the built-in D#-A# or A#-G# scales.

The BOSS Tuner app supports the same audio standards as the TU-3 / TU-3W pedal tuner, which means you can tune to the frequencies used in professional recording studios.