A free program for Android, by HappyDay.

This is a free guitar tuner app that is extremely easy to use. You don’t have to go through any sort of tutorial to get it running. Once you have it up and running, all you have to do is start it, turn the volume up and you can immediately start detecting the string you are playing on. It is extremely easy to use and will allow you to tune your guitar in seconds. It is recommended by guitar teachers and it is the best choice for beginners. This app is very accurate, and it can detect the string automatically. It has a professional accuracy for advanced players.