In case you want to determine webserver and OS information for a given site use curl or wget. Some sites will reveal a lot of information some is not so informative.

# curl -I http://<domain>

# wget --server-response --spider http://<domain>

https can be used as well

If curl or wget is not installed telnet can be used as well

# telnet <domain> 80 (or 443 is https is used)
Type
HEAD / HTTP/1.0
Hit enter twice