https://www.techradar.com/news/best-fitbit-apps-and-watch-faces

When launching the Fitbit Ionic smartwatch, Fitbit took the brave decision to go it alone. Rather than opt for an Android Wear watch offering access to the well-stocked Play Store, it released a watch running its very own operating system called Fitbit OS.

We’ve seen many times in the past how difficult it can be to convince the mobile developer community to embrace platforms outside of the Apple and Google realm (see Windows Phone, BlackBerry, Palm and so on), but Fitbit is off to a decent start.