The Arduino Nano is a compact board similar to the UNO.

The Arduino Nano is a small, complete, 

and breadboard-friendly board based on the ATmega328P (Arduino Nano 3.x). 

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.