The Arduino is an amazing tool for physical computing — it's an open source microcontroller board, plus a free software development environment. Use it to make cool interactive objects that can sense inputs from switches, sensors, and computers — and then control motors, lights, and other physical outputs in the real world. 

 This UNO Clone board (an open source board with all the same properties as the original  Arduino board, only slightly cheaper) is compatible with all current shields and comes assembled — simply connect it to a computer with a USB cable (included) or power it with a AC-to-DC adapter or battery.

 The UNO Clone board is also based on the ATmega328 (datasheet), but features a SMD chip hard soldered to board. It has 14 digital input/output pins (of which 6 can be used as PWM outputs), 6 analog inputs, a 16 MHz ceramic resonator, a USB connection, a power jack, an ICSP header, and a reset button. It contains everything needed to support the microcontroller; simply connect it to a computer with a USB cable or power it with a AC-to-DC adapter or battery to get started.