The Leonardo differs from all preceding 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.
The high Performance, low power AVR® 8-bit microcontroller.
The ATmega32U4 has built-in USB communication that allows the Micro to appear as a mouse/keyboard on your machine.
The Arduino Leonardo features a barrel plug connector, that works great with a standard 9V battery.
The ATmega32U4 features 1kb of EEPROM, a memory which is not erased when powered off.