Nginx is the more common of the two in our index: it runs on 11,573 websites against 5,243 for Next.js, and 610 sites use both. Counts come from real scans, not vendor claims.
Next.js is a React framework for developing single page Javascript applications.
Nginx is a web server that can also be used as a reverse proxy, load balancer, mail proxy and HTTP cache.
610 sites run both Next.js and Nginx. That is 12% of the sites using Next.js, the smaller of the two.
Want to know which one a particular site uses? Look it up and see its whole stack, or compare two sites side by side.