Here at Ipregistry (https://ipregistry.co) we use gulp, nunjucks with custom CSS and Javascript for the landing page. It's quite easy to maintain and static pages are perfect for SEO and fast loads.

The dashboard is a single app page that makes use of lit-html and web components.

The backend makes use of Kubernetes, Cloud Pub/Sub, Cloud Scheduler, Redis, Firestore, Firebase Hosting, etc.

Some parts make use of Cloudflare for CDN purposes.

CI/CD: Cloud build and Travis-ci for open-source clients.

If you are interested by what stack popular websites are using you should have a look at https://stackshare.io.