Watchduino 2 is a smartwatch with an OLED screen, Bluetooth LE to connect to Android apps, and can be mounted with US$ 20 in parts.
It's the successor to the first Watchduino, and I want to believe that this new version will eventually also reach a stage where it can run for weeks between recharges.
As with the first one, all code and schematics are available under free licenses. Unlike the first one, now theres more pixels available on the screen, and the ability to send and receive bluetooth data from an Android smartphone enables the Watchduino 2 to display tweets and the weather, bus times, notifications and even sync the time.
Currently under development by Mar Bartolome (published on Hackaday.io), the Watchduino 2 uses a 3.3V Arduino Pro Mini, a LIPO battery, a small 128x64 OLED display, a vibration motor, a BTLE transceiver and not much else.