Bookly tracks my reading time in books, with a streak tracker
Timehop tracks my streaks of … looking at TimeHop for "on this day" for my tweets and Foursquare Swarm checkins
Swarm tracks daily and weekly streaks for checkins
Ingress tracked a streak of hacking portals. It ended when I forgot to hack a portal when I was working from home all day one day. I had the top badge for it by that point.
Duolingo tracks a daily streak of learning languages
Headspace tracks a daily streak of meditation