This page contains an on-line harmonica tuner Java Applet. I beleive it works well, but no guarantees, use it at your own risk.
You need a Java plugin to run it. It was tested with a few versions of Java and with three operating systems, nevertheless, incopmpatibilities are possible.
Usage is pretty intuitive. It is designed to tune a major diatonic harmonica, but of course you can use it to tune any instruments. It uses "equal tuning" with A = 440 Hz. If you just want a sound of 440 Hz, choose A from the combo box and click on button 4B.
I appriciate any feedback.
E-mail: b i r o c s @ f r e e m a i l . h u