Arduino Leonardo is a pretty new microcontroller board based on the ATmega32u4. 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 power jack, an ICSP header, and a reset button. It contains everything needed to support the microcontroller; simply connect it to a computer with a USB cable or power it with external power supply. Arduino Leonardo code libraries allows the board to emulate a computer keyboard, mouse, and more. Arduino Leonardo comes in two different flavours: with headers and without headers.
The Leonardo differs from all preceding Arduino boards in that the ATmega32u4 has built-in USB communication, eliminating the need for a secondary processor. This allows the Leonardo to appear to a connected computer as a mouse and keyboard, in addition to a virtual (CDC) serial / COM port. And since the communication with the computer is done through a simulated serial port over USB, the hardware serial port on the processor is free for your applications.
There is also another new member in Arduino family. Adafruit’s got a new board, an official Arduino article tells that there’s a new Arduino in town, this time designed in conjunction with Adafruit. It’s the Arduino Micro, a very neat little board designed for breadboard use. The new Micro takes all the best features of the new Arduino Leonardo and shrinks them down to a convenient stick of gum-sized package. It’s powered by the ATmega32u4 microcontroller. Like the Teensy boards (and Arduino Leonardo), the Micro is able to function as a USB keyboard or mouse.
I have not had yet any hands-on experience with those boards, but maybe some day I have. The closest thing I have tried to those is MaKey MaKey board that uses Arduino Leonardo firmware.