ActionScript is a scripting language used for RIAs, mobiles applications, web applications, etc.

ActionScript is a scripting language used for RIAs, mobiles applications, web applications, etc. which was initially developed by Macromedia and then acquired by Adobe. It targets to compile for Flash player runtime which can be deployed in various platforms including mobiles.

From Wikipedia:

ActionScript is an object-oriented language originally developed by Macromedia Inc. (now owned by Adobe Systems). It is a dialect of ECMAScript (meaning it is a superset of the syntax and semantics of the language more widely known as JavaScript), and is used primarily for the development of websites and software targeting the Adobe Flash Player platform, used on Web pages in the form of embedded SWF files.

The language itself is open-source in that its specification is offered free of charge and both an open source compiler (as part of Apache Flex) and open source virtual machine (Mozilla Tamarin) are available.