TUNINGS
A part from the Richter standard tuning system, there are many other possible ways of tuning the diatonic harp.
For a quick but outstanding review on the main tuning possibilities, please check pp. 46-54 in "The Harp Handbook", IInd ed. by Steve Baker, Edition Louis Hermann Demmler, 1995, Germany. This book is a must for every serious harp player.
For a more in-depth look at almost every tuning possibility, please check Pat Missin' "Altered Tunings for the Harmonica" which can be downloaded at Pat's Web Page directly.
Examples of beautiful music played with altered tuned harmonicas can be heard on any of the Richard Hunter' CDs. I strongly suggest "The Second Act of Free Being", by Richard Hunter, Turtle Hill Productions, THP05CD, 1997.