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.
Get approximate IP details.
Get all possible details about an SSL certificate.
Get all possible details about a domain name.
Get details of any file type, such as the mime type or last edit date.
Easily convert nibbles to gibibits (Gibit).
Get the gravatar.com globally recognized avatar for any email.
Check if the URL is cached or not by Google.
Make sure your passwords are good enough.
Get & verify the meta tags of any website.