Hack is not a PHP flavour. It's a separate language that's inspired by PHP, with its own separate interpreter (HHVM). Etsy still uses PHP, as does Vimeo and Wi

Hack is not a PHP flavour. It's a separate language that's inspired by PHP, with its own separate interpreter (HHVM). Etsy still uses PHP, as does Vimeo and Wikimedia. A few other launched-in-early-oughts web properties rely heavily on it too (e.g. Flickr).