ETA might be a bit more popular than watchOS. We know about 1 link to it since March 2021 and only 1 link to watchOS. We are tracking product recommendations and mentions on various public social media platforms and blogs. They can help you identify which product is more popular and what people think of it.
You can find the list of compatible watches all the way at the bottom of this page: apple.com/watchos/watchos-7 (it's right above the SDK section) Hope that helps clear up your confusion! Source: about 3 years ago
ETA. Tells you the current travel time between any two points and has a useful widget. We live south of the city and find it very useful for commuting, especially in the morning. FYI: iPhone and Apple Watch only, in case that’s important. Source: over 2 years ago
InfiniTime - InfiniTime is an open-source, C++-based firmware OS specifically made for the PineTime smartwatch.
Time Map by Mapbox - Rethinking maps based on time to travel
wasp-os - Firmware for smart watches based on the nRF52 family of microcontrollers (including Pine64 PineTime)
Carry - Executive assistant for travel on Slack
InfiniLink - iOS Companion App for InfiniTime and the PineTime smartwatch
Navdy - Heads-Up-Display. Feels like driving in the future.