There are so many apps available that it is difficult to know where to start.
Here are some recommended ones that are worth looking at:

Star Chart – aim your phone at the night sky
and learn more about the universe, space and planets.

Memrise – learn a new language – explore new words and phrases and learn how to speak, read and write in a whole host of languages.
Duolingo – a great fun app for language learning

CamScanner – this app is great for scanning documents on the go into clear & sharp images/PDFs, to email, fax, print or save to cloud.  Just take a photo of the page you need and this app will convert it to a searchable file you can edit.

Moment Diary – plan to keep a diary next year? This app is a useful way to collate creative thoughts and ideas.

There’s lots more apps out there.
Check these websites for more ideas.

http://time.com/4801316/best-apps-2017/

http://www.thetechedvocate.org/tech-edvocates-2017-list-116-best-teaching-learning-apps/

http://www.wired.co.uk/article/best-android-apps-2017