The A-Tuner app is a free Android app for tuning any musical instrument. It has a lot of features like: show rotor, set rotor width, set rotation speed, allow pitch rotation, enable indicators during tuning and snap indicators during tuning. You can use this app on both tablets and phones as the layout is really responsive and the Android version requirements are not so great. You can also set the range of the pitch in this app from C1 to C9 as well as the frequency for the A4 note. The app has 2 main modes: manual and auto. From these two ends you can set the range of sensitivity and also output sound. You can use the app to play the sounds at prespecified frequencies, and this is very interesting at this app. The sounds are outputted through the phone or tablet's own sound system, meaning that for the sounds from this app you can set the volume from the general notification slider (from where you set the volume for the ringtone). The A-Tuner app is a really useful app for tuning any musical instrument that can be tuned, but for pianos, you had better call in a specialist so that you don't get yourself into too much trouble.