At just 18.5 mm by 21.0 mm, the BLE Nano board by RedBearLab is the smallest Bluetooth 4.1 Low Energy development board available. The quarter-size chip is a real power saver and can serve a central or peripheral role in your next project. Supported BLE central devices include those running iOS 7 and 8, as well as those with Android 4.3 and above.
The onboard Nordic nRF51822 operates at 3.3V, but the board can accept anything from 3.3 V to 13 V through the VIN pin and will regulate it appropriately. Alternatively, 1.8 V to 3.3 V of power can be supplied through the VDD. (Don’t apply power via the VIN and VDD at the same time though, unless you’re trying to fry the board.)
That wide range in voltage makes it perfect for a wide range of electronics. Apps can be developed using Nordic’s SDK, mbed.org, or RedBearLab’s open source Arduino Library for the nRF51822.
You can buy the BLE Nano Kit (which comes with the MK20 USB for loading firmware into BLE Nano from a PC) for $37.91 from RedBearLab.