Today’s web apps demand many resources. I have used several technologies to program chanqya.com.
They include PHP as the main programming / scripting language.
MySQL for the database.
AJAX for instant communication between server and client side (browser) without refreshing the page.
An MVC platform (on PHP) for building the app.
Bootstrap for CSS part.
Twig for rendering of HTML pages.
Quill editor for submitting answers, etc.
In addition, open source resources like Magnific Popup, Selectize, PHPMailer, etc., have been used for some specific purposes.
Have also used Hybridauth and Google reCaptcha 3.0, but these are incomplete and will be implemented fully after some time. Social Login through Facebook, Google and Twitter will also be done in the next version. Will also be using AJAX on more pages (right now, it is used on some pages) in the next version so that there is no need to refresh the page for most on-page submissions by users.
Hope this information is useful.