Basic tuner app for tuning musical instruments with features like: Detect pitch based on autocorrelation and FFT spectrum, Accuracy improvement by evaluating the spectrum phase information and polynomial fitting, Show how pitch changes over time, Tuning to equal temperament, Settings for choosing concert pitch, FFT window size, FFT window type, overlap and more
in Open Source Version.

https://www.f-droid.org/en/packages/de.moekadu.tuner/