I could use one for the top register of the bass clarinet.
So could a lot of people. But, unless you get your programming act together and get on the "app" bandwagon, I'd place the chances at slim to none that you're going to see one.
I used to program for the Newton system, and it was all that I could do to keep the uses of the various ({[]}) symbols in line with that. Other than Hypercard/Supercard, I've pretty much given up the programming ghost, which is odd since that was my major during my college years. You don't use it (assembler and RPG were my two main "work" programming languages), you quickly lose it.
The iPhone SDK is free (although there is a charge for registering your programmer identification code). It's the learning curve and the time that's the problem. That Bassoon "app" is a nifty piece of work indeed, but I imagine that there was quite a bit of work done just to get everything just so.
Ironically, I forget my bassoon skills quickly after putting it away. My son, who played the horn back in high school BIH (before ice hockey) hadn't touched one for five years, but when he picked mine up when it was left out during one of his visits, he immediately ripped out the last movement of the Mozart concerto from memory, and with minimal fumble fingering.
True, it's pitched in an easy key and all, but still. Why can't I do that? For that matter, why couldn't I remember all of that bracket crap when programming?