Adobe ActionScript is the programming language of Adobe Flash Platform. Originally developed as a way for developers to program interactivity, ActionScript enables efficient programming of Adobe Flash Platform applications for everything from simple animations to complex, data-rich, interactive application interfaces. The combination of the design and animation tools in Flash CS5 and advanced interactive capabilities of ActionScript 3.0 offers one of the most powerful, most versatile development environments.
Flash Builder 4 (earlier known as Flex builder) also uses ActionScript 3.0.