They were created by a voice trainer who tends to specialise in Transgender voice training, anyway they are a mix of video ( intro's and examples) followed by testing, where you repeat the sounds in turn show in the training video, the tests are ranked and allow you to repeat or if 90% or better (up to you) move on, but if you move on before you are ready, you will tend to fail... There are 5 apps, breathe, pitch, pitch 2, Pitch 3 and Pitch 4... These are the MTF they also have a range for FTM too...
There is a cost, for me in Australia on iPhone they were approx $15 each I think...
I am still on breathing and Pitch 1, because I can't get consistent time on them, and my voice is old and breaks down a bit quicker...
But on the whole they do seem good, I'll keep going, but because of age and how your brain remembers things, i'll opt for surgery as it takes away the risk of fail when when your out of your comfort zone, or cough etc.... But thats my lazy and reasoned excuse

L Katy