Platform: iOS, Android
A tuner is one of the most important utilities a guitarist needs. It doesn't matter if you are an amateur or a professional, carrying a tuner never hurts and it is always wise to do so. GuitarTuna is one such app which allows you to tune your guitar into perfection.
The app uses your phone's microphone to listen to the tune of your guitar and then it goes on to show how off scale each string is. You can select the strings manually or let the app do it for you on automatic mode. The app also offers you different games such as recognising a chord by its pattern or by listening to it which can help beginners to learn and practice.
The app is free but there is also a pro version which will allow you to tune other instruments such as the ukulele. If you have a guitar, it would be wise to have this app installed on your device even as a backup.