Android app for learning German (exclusively) vocabulary?

Question

I'm looking for an app for learning German vocabulary. The app should be available for Android OS and have the following features:

1. Vocabulary learning focused (not a mix of both vocabulary, grammar, etc.) or with a strong focus on vocabulary.
2. Names must be presented with their article (der, die, das). This point is important, otherwise it pretty much makes little sense to learn the word in the first place.
3. Plural forms of names must be displayed with each word.
4. Flash card based learning systems are fine, other vocabulary learning systems are fine as well.
5. Must be working offline.
6. Free is a nice plus.
7. Saves progress is a plus.
8. Words are categorized by levels (for instance A1, A2, B1, etc.), a plus.

Please note that 2 and 3 are really important. If you are not given the gender (or the plural) of a German word, you can't really use it correctly and effectively.

Answer 1

The dict.cc app has a premium vocabulary learning feature, works offline, is focused on vocabulary and shows the gender with the words (so no der die das but m f n).

Unfortunately I don't know about the other points because I don't have premium.