This Original Arduino Micro is similar to the Arduino Leonardo in that the ATmega32U4 has built-in USB communication, eliminating the need for a secondary processor. This allows the Micro to appear to a connected computer as a mouse and keyboard, in addition to a virtual (CDC) serial / COM port. It also has other implications for the behaviour of the board.
Onboard is the processor, crystal, micro USB connection with fuse, Reset button, ISP low-level reprogramming header, ON LED, TX and RX LEDs, an extra user pin #13 LED, and a 3.3V regulator. Youll probably also want to pick up a micro-B USB cable to connect this board to your computer
You can use it for basic Arduino sketches as well as USB client projects like making it appear as a mouse or keyboard to your computer! Although it is not shield compatible it does have all the same pins as a Leonardo. Its best for when you want to shrink your project down or use it on a breadboard.