Google released the source code to the Pebble Watch operating system. Fitbit acquired Pebble's assets in 2016 and Google later acquired Fitbit. 
GitHub
GitHub - google/pebble: This is the latest version of the internal repository from Pebble Technology providing the software to run on Pebble watches. Proprietary source code has been removed from this repository and it will not compile as-is. This is for information only.
This is the latest version of the internal repository from Pebble Technology providing the software to run on Pebble watches. Proprietary source co...