What is the difference between nginx and xinetd ?
When should I prefer nginx, and when should I prefer xinetd?
Maybe I'm wrong, but I got the impressions they are both proxies. I got that nginx does a lot more, but - is there anything xinetd does better?
Nginx is primarily for serving and proxying HTTP request.
Xinetd does neither of things of things. Instead, it is a "super server" that listens for network connections, and launches launches the appropriate service for that request. One use of xinetd would be conserve memory for services that are not access frequently. For example, sometimes people access 'sshd' through xinetd, instead of running 'sshd' continuously.