A couple ones on my list:

Distraction blocker — Chrome extension that helps you block distracting parts of websites (such as the Youtube home page). Sort of a generalized version of Kill News Feed, which blocks the Facebook news feed.

Blue Apron for Hobbies — Helps you adopt a hobby with less of an overhead and research requirement. Bundles up the necessary equipment and information to help you learn the skill, sending you a weekly package and linking to instructional videos.

Lie detection app — See if you can detect lies using computer vision (more of a research project, not sure if it's possible)

Yelp for Github — Chrome extension that lets you rate and view ratings of Github repositories (beyond just the number of stars and forks that Github shows)

Rock climbing app — App that overlays various rock climbing routes onto an image of a rock face using computer vision.