There are already many good tuner apps, such as Cleartune, which I use, or used pretty much all the time, but they only allow you to measure the pitch of one note at a time.
The danger with this is something that I've harped on about in workshops for years. With the flute, pitch is such a volatile thing, so easily changed by temperature, humidity, blowing pressure, and embouchure, that to simply blow a note into a tuner and declare yourself in tune is not really an option.
Commonly, in traditional music circles anyway, the player asks for an A, ( not the best option as a pitch centre for Irish music at the best of times), tunes to it, and then discover that when they begin to play that they are still not in tune. This process can be repeated several times with no better result, because the basic error is that the player is blowing the note differently ( commonly with a different blowing pressure) when tuning than when playing.
The great thing about the RTTATuner is that it samples the notes as you actually play a tune, many times per second, and then gives you a read-out which shows how the pitch of each note (octaves are distinguished) averages out over the time played.
Here's a sample using a keyless flute I was working on yesterday:
This is a screenshot from the phone, which at the moment is the only way you can export the data visually. You do this by pushing the home button and the on/off button at the same time, which saves the screen in photos, and you can then mail this to yourself.
You can see from the above that this flute is fairly much bang on in tune, bar the A and B in the lower octave, which require a little work. Promised updates will make export of data much easier.
There has been a lot of discussion about this app both on Chiff and Fipple and the Earlyflute discussion list, but I think the best thing to do is simply to get it and play with it, and learn more than you ever thought possible about:
How your tuning when you play can vary from day to day, and even tune to tune. With a simple system flute you'll see that internal tuning varies according to what key you're playing in.
with old flutes, just how horrific the internal tuning actually is!
How much slide movement affects the pitch of different notes differently
How by varying your embouchure you can improve the internal tuning ( and overall pitch) of certain flutes
the realtime effect of cork position on octave tuning and pitch.
in short, endless hours of fun....
And of course wearing my makers hat, this is a dream come true.
I should add that the Flutini program did just about the same thing, but written as it was for PC, the Mac version was a source of endless frustration, which didn't have all the features, and was constantly quitting.....so thanks, Dan Gordon, the flute world is beholden to you.