Here lies the source code for a haptic (vibrating) metronome app for the Pebble watch. You can adjust the tempo with the up and down buttons and toggle vibration with the select button.

You can find it on the Rebble app store here. As of October 20, 2018, it's the top search result for "metronome."

My Pebble broke a long time ago, so I am no longer actively developing this application. However, I intend to keep it available and functioning for as long as I possibly can.