Minify your HTML by removing all the unnecessary characters.
Minify your CSS by removing all the unnecessary characters.
Get approximate IP details.
Find A, AAAA, CNAME, MX, NS, TXT, SOA DNS records of a host.
Make sure your passwords are good enough.
Get all possible details about a domain name.
Ping a website, server or port..
Get all possible details about an SSL certificate.