Arduino Uno R3
The advantage of using an Arduino board is that it uses an open-source platform. The schematics of the board are available online. You need an Integrated Development Environment (IDE) to write programs on the board.
The microcontroller used is an ATmega328. The Arduino Uno R3 has 20 digital pins, 6 of these pins are for Pulse Width Modulation (PWM), and 6 other pins for analog inputs. It has a 2.1mm center-positive plug for power and uses a B-type USB connection to upload programs.
You need an Integrated Development Environment (IDE) to write programs on the board. For alternative programming interfaces, the in-circuit system programming or ICSP header can be useful. The Arduino boards have a massive support community that you can access through arduino.cc/forum.