NCH Tone Generator is software that generates a sustained tone at a frequency you designate.  The tone can be a sine wave, a square wave, and a number of other basic waveforms.  Tones can be designates and saved to a list. Playback is with a click on the saved item.  One use would be to setup a just scale and match chanter tuning against that. It’s also a useful reference for drone and regulator tuning.  PC Only.

http://www.world-voices.com/software/nchtone.html