Arduino is an open-source physical computing platform based on a simple i/o board and a development environment that implements the Processing/Wiring language. Arduino can be used to develop stand-alone interactive objects or can be connected to software on your computer (e.g. Flash, Processing, MaxMSP). The open-source IDE can be downloaded for free (currently for Mac OS X, Windows, and Linux).

        The Arduino Nano is a small, complete, and breadboard-friendly board based on the ATmega328 (Arduino Nano 3.x) or ATmega168 (Arduino Nano 2.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. 
The microcontroller (an ATmega328) on the Arduino Nano is a physically smaller version of the chip on the USB Arduino boards.

Features : 

•    ATmega328 microcontroller.
•    Input voltage - 7-12V.
•    14 Digital I/O Pins (6 PWM outputs).
•    6 Analog Inputs.
•    32k Flash Memory.
•    16 Mhz Clock Speed.