Flask / Python – We used Flask initially to power our API, but we liked it so much that we started to move most of our critical backends to it. Flask’s flexibility allows us to swap front-ends from Handlebars (used in emailing) to ReactJS (used in rest of applications) without much hassle.
React – We use ReactJS to built most our critical applications. Most of our React components are stateless, and we have created our own flavor of Redux/Flux, as well as routing, over the years.
Node – We use Node mainly for server-side rendering. We run it as a side process for Flask to communicate to and don’t actually expose node externally.
Statamic / PHP – We use Statamic to build and serve a lot of our static content pages, including internal Q/A sites, and external public pages, such as our team, and contact pages.
AWS Lambda – We use Lambda to handle a lot of file processing, such as image rotation/resizing, PDF generation, and producing quick previews of webpages that our users might link to.