Minify your HTML by removing all the unnecessary characters.
Minify your CSS by removing all the unnecessary characters.
Ping a website, server or port..
Find A, AAAA, CNAME, MX, NS, TXT, SOA DNS records of a host.
Get approximate IP details.
Get all possible details about a domain name.
Make sure your passwords are good enough.
Check if the URL is cached or not by Google.