Facebook still uses PHP heavily. Technically it's a language called "Hack" (PHP augmented with some nice modern features), and runs either on HHVM (JIT: PHP/Hac

Facebook still uses PHP heavily. Technically it's a language called "Hack" (PHP augmented with some nice modern features), and runs either on HHVM (JIT: PHP/Hack -> C -> binary) or precompiled to binary.