Flyfit is a very nice invention for the people who are really like exercise like Cycling & Swimming. It is
Smart Ankle Tracker For Fitness, Cycling & Swimming.

Flyfit is a smart band that measure your leg movements, monitor your physical activity and displays your performance in real-time. Whether is all about, distance, speed, pedal cycles, calories burnt and duration. These are all can tracked on your tablet device and smartphones.

I think this tracker make the exercise time more enjoyable. I really like it. Thanks, @hazelalex for your nice hunt.