This chromatic tuner app for Android phones can be used with any acoustic instrument. The interface adopts a very clean-looking and readable “virtual VU meter,” with a needle that shows whether you''re flat, sharp, or dead-on. Other modes include orchestra tuning (user-redefining of frequencies); just, Pythagorean, meantone, and comma temperaments; a variable-range nonlinear scale; microphone-sensitivity adjustment; a pitch pipe (tone generator); and more. The free version has all the features of the full app but includes ads. If you fork over $2, the ads go away.