Pebble

 Pebble  or the Pebble Watch was a smart watch that pairs to a mobile device via Bluetooth LE, and provides a very minimal low resolution black&white text & pixel display, has passive sensors (3D accelerometer, compass, ambient light), a vibration motor and four buttons. On 2016-12-07 Pebble announced they're shutting down and no longer manufacturing devices. 

The manufacturer currently supports interfacing with the iOS and Android operating systems.

App Store
Pebble announced on 2014-01-06 that they would be launching an app store. Pebble, from the beginning, has supported apps written in C with the use of their SDK. Many of these apps required the use of companion apps on the connected phone.

Since version 2.0 of the API, a javascript library permits Watchapps to access phone functions and the Internet directly.

Criticisms

 * Pebble is limited to the installation of 8 watchfaces/watchapps.

Aaron Parecki
uses a Pebble with aaronparecki.com to:
 * sign-in to his site, this wiki using IndieAuth with TOTP on the Pebble since 2013-07-15
 * publish food posts on his site using his Teacup app for Pebble since 2014-10-03

David Shanske
has used a Pebble since 2013-12-16:
 * to receive notifications of webmentions using Pushover since initial purchase

Tools

 * TOTP sign-in with IndieAuth - http://aaronparecki.com/articles/2013/07/15/1/password-less-logins-from-your-own-domain-with-a-pebble-watch
 * Teacup