Minify your HTML by removing all the unnecessary characters.
Minify your JS by removing all the unnecessary characters.
Extract email addresses from any kind of text content.
Find A, AAAA, CNAME, MX, NS, TXT, SOA DNS records of a host.
Take an IP and try to look for the domain/host associated with it.
Get approximate IP details.
Get & verify the meta tags of any website.
Make sure your passwords are good enough.