The latest addition to the Arduino family is here! The Arduino Leonardo is a microcontroller board based on the exciting USB-enabled ATmega32u4 (datasheet). This chip has about the same amount of flash, RAM and capability as the ATmega328 found in the UNO. It has 20 digital input/output pins (of which 7 can be used as PWM outputs and 12 as analog inputs), a 16 MHz crystal oscillator, a micro USB connection, a spot for a 2.1mm power jack, an ICSP header breakout, and a reset button. It contains everything needed to support the microcontroller; simply connect it to a computer with a USB cable to get started.
The Leonardo differs from all preceding boards in that the ATmega32u4 has built-in USB communication, eliminating the need for a secondary chip (such as an FTDI friend, FTDI cable or the USB/Serial converter on the UNO). On one hand this means that sketches on the Leo are a little bigger because it's also handling USB interaction. On the other hand, it allows the Leonardo to appear to a connected computer as a mouse and/or keyboard, in addition to a virtual (CDC) serial / COM port. It also has other implications for the behavior of the board; these are detailed on the getting started page.
We're very excited to have a small shipment of Leo's in stock. Please note that this board is very new and so is best used by people with existing Arduino experience as there may be a bug that trips up beginners. It is probably not going to work with nearly any shields other than the proto shield. We haven't gone through and tested it with all the Adafruit shields and don't guarantee it will work until we've sat down and done a lot of testing and coding, so keep that in mind!
This board is only supported in the latest Arduino IDE 1.0.1 so you will also need to update the IDE.