Idea #1) Safemap Pull crime blotter data, and deliver the least dangerous route between two locations. Offer a "danger score" for locations.

Idea #2) Health Tracker with Correlations There are a lot of self-tracking apps out there; few to none of them do what the actual point of a self-tracking app is, which is to identify correlations between what you're tracking. (e.g. are you unhappier when you get less sleep?)

Idea #3) International Video Pen Pals Practice learning the language of your choice by being paired with a native speaker for video chat.