FitbitOS by Fitbit

FitbitOS is Fitbit's smartwatch platform created on the heels of the company's acquisition of Pebble. It is an operating system that is powering the Fitbit Ionic and Versa watches, providing users with a number of features, such as music playback, contactless payments (Fitbit Pay), notifications and alerts. Perhaps most important is the fitness tracking capability that includes personalized workouts and coaching. FitbitOS supports custom clock faces and its functionality can be extended with third party apps that are available from the Fitbit App Gallery.