Unlike other open source announcements, the code isn’t available just yet. It will be released next month on GitHub as ChakraCore. ChakraCore won’t be the exact same version that is in the Edge browser and for good reason. While features like asm.js and ECMAScript 2015 support will be included, much of the code that stitches the Chakra engine to the Edge browser’s HTML rendering will be removed and new diagnostic APIs will be built for ChakraCore that don’t use COM. This diagram shows the key pieces being open sourced (in purple).
Currently this code will be targeted at Windows only but Microsoft will be working to extend this to other platforms as well including having already built a version of Node.js that uses Chakra instead of Google’s v8 engine.