Android's Open-Source Instrument Tuner
Noteworthy Tuner is, as far as I can tell, the first open-source instrument tuner for Android™. It is also the only one, to my knowledge, that is both free and ad free. While the other tuners require the user to pay in order to remove ads, Noteworthy is always free of ads.
Noteworthy is simple by design. Simply launch the app and tune your instrument. There is no need to select which string or note you wish to tune—the app automatically determines that for you.
For a full list of features and many screenshots, please see the listings on Google Play™:
Try the free app:
Noteworthy Tuner is an open source project. Source code is available on GitHub.