1. A GitHub app that lets you browse through all of the repositories on the site. It would also allow you to save repos to be viewed later.
2. An SSH terminal app that allows to connect and issue commands to your server. It would have the same look and feel of terminals that you find on your computer.
3. A guitar utility app. It would be able to show you all the scales, chords, and have a built in tuner that would use the microphone to detect pitch. The tuner part might be a bit complicated to code.
4. A to-do list/reminder app. It would be very basic and have a clean interface. A lot of the other apps I see have too many features and it makes the app seem bloated.
5. An app that uses the GPS on phone in some way. Like an app that would remind of something when you arrive at a location.