You can pretty much Google anything now including a Guitar Tuner FOR FREE!
That's right now Google has their own Guitar Tuner that you can find HERE and it will use your microphone to help keep you in tune you have to search for “Google Tuner” specifically.
The feature is called “Google Tuner,” and it will use your computer or phone microphone to listen to the sounds coming out of the guitar and tell you whether they’re in tune. Android Police report a similar functionality existed before and you could invoke it by telling Google Assistant to “tune my instrument,” but now it’s available as a search phrase and works from any device.