ActionScript is an object-oriented programming language originally developed by Macromedia (now dissolved into Adobe Systems). Its latest version is ActionScript 3.
It is used to create web applications (including RIAs), desktop applications and mobile applications. The web target is served using the Adobe Flash Player runtime, while the desktop and mobile targets are served using the Adobe AIR (previously Adobe Integrated Runtime).
Popular IDEs are Adobe Animate (rebranded from Adobe Flash), Adobe Flash Builder, FlashDevelop, IntelliJ and others.
Some of the popular compilers are Adobe Animate, Apache Flex, Haxe, OpenFL and others.
Adobe Scout and FlashFirebug can be used to debug the Adobe AIR and the Adobe Flash Player runtimes.