HSK Chinese Learning Assistant is a comprehensive app for learning for the HSK exam.

It contains all required phrases for all six level of HSK.
You can test your knowledge of Chinese using either Flashcards or multiple answer tests. There are four learning modes: Chinese-to-English, English-to-Chniese, PinYin, Tones.

You can build your customized list of phrases that you want to focus on. You can then run flashcards, multiple answer test on it or export the list.

App additionally offers built in dictionary, searchable using pinyin or Chinese characters.

Chinese Web Reader - an embedded web browser, which upon touching Chinese text shows pop-up with character explanation.

Chinese Text Reader - for pasting Chinese text from clipboard or reading from text file and showing pop-up with character explanation.

All phrases can be pronounced by the app, using TTS engine.

You can backup and restore your progress, when you need to reset your device or you need to move app to new device.

The best at the end; the app comes for free.
There are some slightly annoying ads, but you can also get rid of them by a very small fee.