EDITORS CHOICE: Loop - Habit Tracker No Ads. No paid add-ons. A clean  tidy interface and great selection of widgets. Easy to use to track habits (or other regular activity). This should be a Google Play Store Editors Choice recommendation. Thank-you to the developer - I don't think anyone would begrudge a yearly pop-up asking for an app review or donation towards continued development of the app.
January 15 2017