Guitar Tuner Free is an excellent app that costs nothing to use, and it will help keep your guitar in perfect tune. The app is fast and highly intuitive, and it requires little operation on the part of the user.

This tuner is capable of tuning standard guitars of either 6 or 7 strings. It can also tune in Drop D, Drop C, and it offers 4-string bass tuning. You can even tune a Ukulele with this app.

Once you open the app, tuning is quite simple. You can either select the string you need to tune, or you can simply start strumming a string and the app will automatically determine which string it is. This obviously works best for strings that aren't horribly out of tune. For instance, if a string is incredibly out of tune, the automatic detection might assume the string is actually a different string.

The tuner itself is fairly straightforward. As you play the string, the app will show you a gauge with the proper tuning in the center. Your goal is the alter the tension on the string so that the tuner aligns with this center segment. You can set the microphone volume on your device to optimally catch sound, but the device will automatically set the microphone to a level that ignores ambient sounds.