Loop Habit Tracker

Ad-free, open-source, and on-device, with a large and long-standing following behind it, which is a lot of trust for something this simple. The flip side is that it does one thing, habit streaks and charts, and does not try to be a planner or journal, so heavy goal-setters will outgrow it. That focus is the appeal: pick it when you want clean habit tracking on Android with no account and no upsell, and look elsewhere if you need reminders tied to a full task system.