I were searching for an app to English classes and I found "Speak English". This app helps you to have a better pronunciation. You choose a topic or a sentence and you heard the correct pronunciation of that, then you record you voice saying the same sentence and you compare. You can repeat this as many times as you like, until your pronunciation is perfect.
I think this app is very practice because you can learn to speak, other apps teach you to write but not to speak.