It's the Arduino Nano without header pins! This version doesn't come with header pins populated so that you can solder in any connector or wire. All of the functionalities are the same as
Arduino Nano.
Arduino Nano overview:
Arduino Nano is a surface mount breadboard embedded version with integrated USB. It is a smallest, complete, and breadboard friendly. It has everything that Diecimila has (electrically) with more analog input pins and onboard +5V AREF jumper. Physically, it is missing power jack and power select jumper. Since the Nano is automatically sense 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 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). Its a four-layer board with power and ground planes to help provide ICs with sufficient charge during switching and reduce noise (EMC) on high speed switching I/O pins. Ground plane help reduce radiation (EMI). Power plane is low in inductance; therefore any transients that may develop on the power line will be at lower levels.
You end up paying less with Nano than Mini and USB combined!
Specifications:
Microcontroller
 
Atmel ATmega168
Operating Voltage (logic level)  5 V
Input Voltage (recommended)  7-12 V
Input Voltage (limits)  
6-20 V
Digital I/O Pins
 
14 (of which 6 provide PWM output)
Analog Input Pins
 
8
DC Current per I/O Pin
 
40 mA
Flash Memory
 
16 KB (of which 2KB used by bootloader)
SRAM
 
1 KB
EEPROM
 
512 bytes
Clock Speed
 
16 MHz
Dimensions
 
0.73 x 1.70
Features:
Automatic reset during program download
Power OK blue LED on the bottom
Green (TX), red (RX) and orange (L) LED
+5V to AREF jumper
Auto sensing/switching power input
Small mini-B USB for programming and serial monitor
ICSP header for direct program download
Power OK blue LED on the bottom
Standard 0.1 spacing DIP (breadboard friendly)
Manual reset switch
Power:
The Arduino Nano can be powered via the mini-B USB connection, 6-20V unregulated external power supply (pin 30), or 5V regulated external power supply (pin 27). The power source is automatically selected to the highest voltage source.
See Nano in action: http://www.youtube.com/watch?v=FJR5wqiGLjM
Documents:
Arduino Nano User Manual (schematic and more pictures)
Eagle design files (unrouted)
note: since the free version of Eagle does not handle more than 2 layers, and the Nano is currently 4-layer board, We publish it here as unrouted, so users can at least open it and use it in the free version of Eagle.
ATmega168 datasheet
Arduino Home Page
Programming Reference
Arduino Forum
