Asteroids
Asteroids is a free operating system for smartwatches from various manufacturers, based on OpenEmbedded, libhybris and Qt5.
AsteroidOS reveals the potential of your watch, providing up to 48 hours of battery life and a set of applications, including everything you need for a smartwatch: an agenda, an alarm clock, a calculator, a music controller, settings, a stopwatch, a timer and a weather forecast application.
☝🏻And all this is open source, unlike the pre-installed proprietary OS of the corporation.