Ardweeny; the smallest Arduino you can solder yourself with through-hole components! And remember folks this is a kit so some assembly is required and batteries are not included :).

This is a backpack printed-circuit board the fits on top of an Atmel ATmega328P straddling it. Solder the pins to the microcontroller's legs, and you're ready to join the open-source hardware revolution!

Fit this little guy pretty much anywhere, just add 2.7V-5.5V for power and you are on your way. 3.3V or 5V voltage regulator is recommended for stable sensor readings but the choice is yours.

Features:

Fully Arduino-compatible! (Select "Arduino Uno" when programming)
Stacks onto the back of an ATmega328 chip (included)
Takes same 28-pin footprint as the microcontroller itself!
Features Pin-13 LED and reset button
Simple construction - only 7 parts plus pins & PCB!
Ideal for breadboard applications

Note: Requires external USB-to-TTL FTDI-type cable or adapter

Also Note: This product now comes with the Arduino 1.0 optiboot bootloader programmed into it. When programming via the Arduino IDE please select "Arduino Uno" under the Tools -> "Board" category instead of "Arduino Duemilanove w/ ATmega328". This bootloader not only has faster upload speeds but is now backwards compatible with products that use a FTDI USB-TTL converter chip.

Interesting side-note: You can also mount your Ardweeny into the socket of a standard '328-based Arduino board, and use the board to program the Ardweeny. The crystal on the main board co-exists with the one on the Ardweeny well enough to let it happen! Handy for when you need to reburn a boot-loader, or you're short on FTDI adapters!