Correct Answer : Facebook
Hack was introduced "facebook" in March 20, 2014. Before the announcement of the new programming language, Facebook had already implemented the code and "battle tested" it on a large portion of its web site.
Hack is designed to interoperate seamlessly with PHP, which is a widely used open-source scripting language that has a focus on web development and can be embedded into HTML. A majority of valid PHP scripts are also valid in Hack; however, numerous less frequently used PHP features and language constructs are not supported in Hack.
