We've talked a lot about the "don't break the chain" method of building habits over the years, where you visually mark the completion of a habit every day to help you build it. The classic method is to put an "X" on a paper calendar every day. The longer your streak goes on, the more motivated you are to keep it going—as anyone with Snapchat streak with a friend knows.
Paper is fantastic for this, granted, but some people prefer digital tools. That's why I like Habo, an open-source habit tracking app for Android and iPhone that couldn't be simpler. There are no ads and no upselling—it's just a way to help build habits. Once you've downloaded and opened the app, add as many habits as you like. The idea is that you will check things off as you do them.
There's an indicator on the top of each habit that lets you know how many days your streak has lasted. And you can configure the settings to do things no paper calendar can, like reminding you about your habit every day at a particular time. For example: You want to start doing 20 pushups before lunch every day. You can set the application to send you a notification right at 11:55. You can also add specific details about your routine and the reward you'll give yourself after completing it.
What I really appreciate about this app is its simplicity—and the fact that it's completely free. Too many productivity tools become needlessly complicated as they pursue monetization. Habo does what you need it to do and nothing else.