The Fio v3 is a new spin on the Arduino Fio hardware powered by the ATmega32U4. While the Fio v3 is not yet compatible with the Arduino v1.0 IDE, it's still a very capable XBee-ready development board.
The JST-connector and 3.3v system voltage make this a great development tool for portable devices, simply plug in a Li-Poly battery and you're ready to go. Wireless sensor networks and communication are made easy by the on-board XBee socket.
The ATmega32U4, running at 8MHz, makes it possible for you to use the on-board USB jack not only to charge a connected Li-Poly battery but to actually program the device! Because this board uses a similar bootloader to the one on the Pro Micro, you will need to download and install the special software driver below. There's also a board definition add-on for the Arduino IDE which will add support for this board.