This website would not be possible without a large assortment of technologies.
All of the code that handles, identifies, and responds to the requests sent from your web browser as well as code that performs periodic or asynchronous background processing to maintain this site runs on top of Google App Engine, which is a part of the larger Google Cloud Platform. While, as a Googler, I am obviously biased, I highly recommend you check out the Google Cloud Platform and Google App Engine; using App Engine both simplifies the process of running a website and, at the same time, makes the website more robust and fault tolerant.
The code that runs on the server that your browser is talking to is written in the Python programming language. Python is a language that is both easy to use -- the code reads much more similarly to English than other languages, so much so that I have ocassionally joked that Python is my pseudo-coding language of choice -- and also extremely powerful. Because Python is interpreted (meaning that the code is evaluated by a program called an interpreter rather than translated to binary, first, and then run by the machine), one can see the results of a change much more quickly than with a compiled language and thus it is particularly well-suited for quick iteration and prototyping. This quick turnaround time is why I selected Python for my website.
Jinja2 is a templating engine (think replacement or substition of data in a pre-made template) for Python. Jinja2 was an obvious choice because it supports auto-escaping, an important security feature, and is very easy to set up within the App Engine environment. It also has an active developer community, has syntax and capability similar to Django templates but without other parts of the Django framework that I don't need, among other features.