The Gmail web interface also (re)invented AJAX. The number of web applications that used XMLHttpRequest increased exponentially after the success of Gmail.
Not the original version. The current version is a hybrid of code compiled from Java (J2CL, previously GWT) mostly business logic shared with Android, iOS, and the server backends, and a UI that is built with Closure Library. It's monolithically compiled and globally optimized via Closure Compiler.
