This Arduino Nano is Original Arduino Nano Board. It is a breadboard-friendly board based on the ATmega328P from Arduino officials made in Italy. It has more or less the same functionality of the Arduino Duemilanove, but in a different package. It lacks only a DC power jack and works with a Mini-B USB cable instead of a standard one.
Original Arduino Nano is a surface mount breadboard embedded version with integrated USB. It is the smallest, complete, and breadboard-friendly. It has everything that Diecimila/Duemilanove has (electrically) with more analog input pins and onboard +5V AREF jumper. Physically, it is missing power jack. The Nano is automatically sensing and switch to the higher potential source of power, there is no need for the power select jumper.
Nanos got the breadboard-ability of the Boarduino and the Mini+USB with a smaller footprint than either, so users have more breadboard space. Its got a pin layout that works well with the Mini or the Basic Stamp (TX, RX, ATN, GND on one top, power and ground on the other). This new version 3.0 comes with ATMEGA328 which offer more programming and data memory space. It is two layers. That makes it easier to hack and more affordable.