Arduino IDE
Description
The Arduino software (IDE) is a free, open source program that allows users to easily write programs and upload them directly to any Arduino-based system. It is generally based on a variation of the Processing platform, and the two can often be used in tandem for working with Arduino systems. There are many online repositories of open source Arduino code that can be used as a basis for any program users may want to construct.
Availability
Arduino IDE is open source software, anyone can download and install it for free on their personal computer.
http://www.arduino.cc/en/Main/Software
Getting Started
Tutorials are available at http://www.arduino.cc/en/Guide/HomePage
Other Resources
The Arduino Forum is a great place to ask questions about making a project work.