Pebble ran third party native apps (generally written in C) sandboxed via the ARM SVC/USR-mode privilege system, integrated with the onboard MPU.
Fitbit - after hiring many Pebble staff - supports third party apps written in JavaScript. These run on the pre-existing JerryScript engine, and are still sandboxed on the native side should the VM have holes. This made it much easier to get started as a developer, but imposed an upper limit on app performance vs. the native apps seen on Pebble.
Fitbit - after hiring many Pebble staff - supports third party apps written in JavaScript. These run on the pre-existing JerryScript engine, and are still sandboxed on the native side should the VM have holes. This made it much easier to get started as a developer, but imposed an upper limit on app performance vs. the native apps seen on Pebble.