If you made it this far you must be serious if you completed the above activities so here are some apps to further your knowledge. I don’t know if these apps are for android, though, sorry.
The Apps are:
Grid Diary by Sumi Interactive (this isn’t Korean, but it can be set to Korean.It might be good for writing practice)
K-Tongue by DaeHyun Choi
Idiom Attack by Exile Express
Korean Numbers by Sakurako Ogata
Korean Alphabet Pronunciation by Yaogao Wu
Korean Postpositions by Minsik Kong