[projektfu]

Every activity is basically a mini app. Take a gym log for example. It has an activity for recording an exercise. It also has an activity for viewing the list of exercises in a workout. It has an activity for viewing a list of workouts. It has activities for editing each of those lists, discovering new workouts, watching videos of exercises, taking notes on particular sets, and adjusting settings. Maybe it includes social features, graphing, reporting, etc. But whoever wrote it started with just a couple of activities and grew it up.