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.
Make sure your passwords are good enough.
Get details of any file type, such as the mime type or last edit date.
Get the web-host of a given website.
Check if the URL is cached or not by Google.
Get & verify the meta tags of any website.
Check if the URL is banned and marked as safe/unsafe by Google.