Android/iOS: We've talked about the benefits of interval training on a stationary bike before. Interval Clock is a customisable interval training app that will get you started quickly, help you find an effective workout, and still leave you free to switch things up as you choose.
Full disclosure: Interval Clock was built by former Lifehacker writer Adam Dachis, and we've highlighted an old version before. The new version brings a number of new features and improvements. Once installed, the app initially guides you the standard 12-second slow/8-second fast interval workout 60 times for a full 20 minutes. You can run with that, or you can customise the slow and fast intervals yourself, or change the number of intervals to suit the amount of time you have to exercise.
Similarly, the screen changes colour now between intervals, so you don't have to have your eyes glued to the screen to know when it's time to pedal hard versus pedal slowly. The app also now remembers your preferences and will stick to the interval times and durations you select. Interval Clock is free, and ad-free. Hit the links below to give it a try.