Apache Flex, formerly Adobe Flex, is a software development kit (SDK) for the development and deployment of cross-platform rich web applications based on the Adobe Flash platform. Initially developed by Macromedia and then acquired by Adobe Systems, Adobe donated Flex to the Apache Software Foundation in 2011 and it was promoted to a top-level project in December 2012. The Flex 3 SDK was released under the MPL-1.1 license in 2008. Consequently, Flex applications can be developed using standard Integrated development environments (IDEs), such as IntelliJ IDEA, Eclipse, the free and open source IDE FlashDevelop, as well as the proprietary Adobe Flash Builder. In 2014, the Apache Software Foundation started a new project called FlexJS to cross-compile ActionScript 3 to JavaScript to enable it to run on browsers that do not support Adobe Flash Player and on devices that do not support the Adobe AIR runtime. In 2017, FlexJS was renamed to Apache Royale. The Apache Software Foundation describes the current iteration of Apache Royale as an open-source frontend technology that allows a developer to code in ActionScript 3 and MXML and target web, mobile devices and desktop devices on Apache Cordova all at once. Apache Royale is currently in beta development stage. Overview Flex uses MXML to define UI layout and other non-visual static aspects, ActionScript to address dynamic aspects and as code-behind, and requires Adobe AIR or Flash Player at runtime to run the application. Versions Macromedia Flex 1.0 and 1.5 Macromedia targeted the enterprise application development market with its initial releases of Flex 1.0 and 1.5. The company offered the technology at a price around US$15,000 per CPU. Required for deployment, the Java EE application server compiled MXML and ActionScript on-the-fly into Flash applications (binary SWF files). Each server license included 5 licenses for the Flex Builder IDE. Adobe Flex 2 Adobe significantly changed the licensing model for the Flex product line with the release of Flex 2. The core Flex 2 SDK, consisting of the command-line compilers and the complete class library of user interface components and utilities, was made available as a free download. Complete Flex applications can be built and deployed solely with the Flex 2 SDK, which contains no limitations or restrictions compared to the same SDK included with the Flex Builder IDE. Adobe based the new version of Flex Builder on the open source Eclipse platform. The company released two versions of Flex