Ask HN: Ideas For Beginning Mobile App Developers?

Recently there was a submission about Ideas for Beginning Web Developers (http://news.ycombinator.com/item?id=2757467).

I'll be grateful if, on similar lines, you could pitch in with some app ideas for beginning mobile app developers.

While I'm not new to mobile app development, most of my work has been on apps that have been quite similar to each other (2D games and barcode apps), and so my mobile app dev experience is quite narrow at the moment. If you could suggest some diverse app ideas, working through them would help me become a more well-rounded developers. Also, it would be useful to others who are truly beginners to mobile app development.

Thanks!