Chinese Pronunciation App
I highly doubt it's a good idea to rely on such apps. Try to mimic high quality recordings or even record yourself for comparison purposes.

Forvo is good for words and phrases, textbooks with an audio CD like Integrated Chinese, Učebnice čínské konverzace and such for whole sentences.

You can also try if some machine translators will get what you're saying by voice, but only for the lulz.