Absolatido shows what notes you are singing or playing...
With Songsolatido you will learn singing at first sight...
With Singsolatido you will practise singing intervals...
With Falling Keys you will learn the names of the keys of a piano...
Absolatido, singsolatido and Falling Keys are apps for both Android and iPhones.
Songsolatido is only available on the App Store
This website in dutch 