An android accordion tuner with strobe and multiple notes. The Windows, Mac and the Android version of this project are also on Google code. The app is available on F-Droid and here. See the Wiki or the app help screen for detailed documentation.
Hold the phone/tablet near the instrument, play a note and observe the display. In portrait the app shows a scope with the input signal, a spectrum showing the processed signal, the main display with the note value, cents error, frequency error etc, a strobe display and a meter display showing the cents error. In landscape the app shows just the main display and the meter. There is a signal indicator in the action bar which is useful in landscape mode.