Lately I've been experimenting with apple wood as tonewood. It compares in density with cherry, a bit softer than maple, beautiful color, and is stiff and musical when tapped.
Apple tonewood is all but impossible to come by. About 6 years ago I had a huge (almost 4' diameter) apple felled in my back yard. I had it milled and dehumidifier kilned, and then it air dried for about 5 years. Just now, it is coming into it's own sound-wise- I resawed a piece of it and the nice tap tone made me want to try building with it.
Here is an Irish bouzouki I recently built with the apple from my yard.:
The sides bent easily and the wood has a smooth surface feel that takes finish beautifully. I am also encouraged by the tone- I would say it is more in the warm type of tonewoods like mahogany or walnut, but it also seems to have clarity and sustain in the high register. It's actually right in the pocket of what I seem to go for- granted design, bracing and top wood play a much more substantial role in the equation, but the apple seems well suited for stringed instruments.