The Arduino Nano Compatible is a small, complete, and breadboard-friendly board based on the Adruino Nano 3.0. 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 USB cable instead of a standard one.
The Nano is automatically sense and switch to the higher potential source of power so there is no need for the power select jumper. Nano's got the breadboard-ability of the Boarduino and the Mini+USB with smaller footprint than either, so users have more breadboard space. It's 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 make it easier to hack and more affordable. You end up paying less with Nano than Mini and USB combined!