Android: Habits are difficult to adopt, so it's important not to overload this hard process with a complex app. Technology needs to get out of the way. That's what Streaks does.
Streaks is as simple as a habit tracking app can get. It works on the "Don't Break The Chain" productivity method. Add a task and the app will ask you every day if you completed the task or not. The free version has a limit of five tasks, while you can unlock unlimited tasks for $US2.
Users can also add a daily reminder for each task, which will show up as a notification. Initially, this feature is a little difficult to get used to. You get the reminder to perform the task, but Streaks also prompts you to say whether you completed it or not. A good idea is to set the reminder for 10 minutes after you will regularly begin the task. If you've already started, there's a good chance you will finish it and so you can mark it as "completed".
Streaks is Android-only. If you're looking for a Web or iOS app, Chains.CC is a gorgeous habit tracker for those platforms.
Streaks (Free) [Google Play Store]