Cost: Free
Zero is a basic tracker that allows you to choose a daily fasting method such as 16:8, a 13-hour circadian rhythm fast (where you start fasting close to sunset), or a fasting period up to 24 hours. There's a clock that counts down or up (you choose) and tracks the number of hours you've fasted for the past seven days. This app is simple and easy to use.
It's a great tracking app if your fasting schedule stays the same every day, and can be helpful if you're trying to stick to daily intermittent fasting. I wouldn't use it if your daily fasting duration changes from day to day. One helpful feature is that it sends notifications to your phone or Apple Watch about your fasting start and end times to keep you accountable