Arduino is an open-source physical computing platform based on a simple i/o board and a user friendly 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, PD).

Duemilanove is the enhanced release of Diecimila version. It adds to the previous new features (autoreset function, extended power connector, built in led, USB overcurrent protection) the automatic power selection.

Board comes fully assembled and tested with ATMega328 pre-loaded with bootloader.

Wikipedia: Arduino-Platform

Arduino Duemilanove Details

Arduino Homepage