Tracking the Days allows you to track the number of days since or until a certain date. You can use it to countdown to a special event (Christmas, anniversary, moving day, graduation, etc.) or to track how long it has been since a certain day, such as positive habits like how long since you quit smoking, started a diet or any other streak you'd like to track.
You can enter the dates to track manually or import them from your calendar. Add the most important date as a widget to your home screen to keep it front and center.