Hey Maine! Thank you for the question!
My framework of choice for the back-end is Ruby on Rails (and consequently, the language is Ruby).
Reason is because it’s very easy and fast to build powerful web apps, Ruby is very pleasurable to code in because of the English syntax, and because the Ruby/Rails community is pretty large and active. I also use it because Ruby on Rails is a framework that many startups in the Bay Area use. In my opinion, it makes sense to get a hang of the languages and frameworks that many startups require of their potential employees :).
And of course, there is no web app without the use of HTML and CSS.
So the languages in my main stack are HTML/CSS/JS/Ruby on Rails!