One idea is to help a user make a choice by presenting pairs of options one at a time. Another is to ask a user custom questions on a schedule and track/graph the results. A third is to make a game like Concentration or Solitaire, but with some unique mechanics.
Sep 4, 2018
Study physics like Susan Fowler
Guide available here. She recommends the Feynman lectures to awaken interest, which are available on-line.