Minify your HTML by removing all the unnecessary characters.
Minify your CSS by removing all the unnecessary characters.
Get approximate IP details.
Take an IP and try to look for the domain/host associated with it.
Find A, AAAA, CNAME, MX, NS, TXT, SOA DNS records of a host.
Ping a website, server or port..
Get all possible details about an SSL certificate.
Get all possible details about a domain name.