Note: 1st-time users please visit Getting Started with Arduino :)
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 Uno is a microcontroller board based on the ATmega328. It has 14 digital input/output pins (of which 6 can be used as PWM outputs), 6 analog inputs, a 16 MHz crystal oscillator, 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 an AC-to-DC adapter or battery to get started.
"Uno" means "One" in Italian and is named to mark the upcoming release of Arduino 1.0. The Uno and version 1.0 will be the reference versions of Arduino, moving forward. The Uno is the latest in a series of USB Arduino boards, and the reference model for the Arduino platform.
Additional features coming with the R3 version are:
ATmega16U2 instead of 8U2 as a USB-to-Serial converter.
1.0 pinout: added SDA and SCL pins for TWI communication placed near the AREF pin and two other new pins placed near the RESET pin, the IOREF that allow the shields to adapt to the voltage provided from the board and the second one is not connected pin, that is reserved for future purposes.
Stronger RESET circuit.