I can quit hinting obliquely about what I've been up to. What started out years ago as a web app, then became a Mac app, then slipped to the back burner until the iPhone came out, is finally available, as a free iPad app.
It's called RatioKey, and it's free!
You can see a page about it on Apple's website by following this link...
Click on the "View in iTunes" link to open iTunes directly to it. (The iTunes application is necessary to download the app and install it on an iPad.)
RatioKey opens to a very different kind of musical keyboard, one that offers 105 distinct tones over a two-octave range.
Each tone is defined by a relatively simple integer ratio. The integers comprising those ratios are themselves defined in terms of the powers of the first five prime numbers (2, 3, 5, 7, & 11).
This becomes clearer if you spend a little time playing with the picker on the Options screen, which alters the
frequency of the center "1/1" key, and with it the two-octave range.
If you have an iPad, be sure to check it out!
PS... If you're wondering what this all has to do with music, I will doubtless do my best to explain, but really I'm an obsessed amateur, not an expert, and must defer to David Doty and recommend his publication, The Just Intonation Primer.
PPS... Feel free to enter any questions as a comment, to this or any subsequent post.