Get approximate IP details.
Find A, AAAA, CNAME, MX, NS, TXT, SOA DNS records of a host.
Get all possible details about an SSL certificate.
Get all possible details about a domain name.
Ping a website, server or port..
Get the gravatar.com globally recognized avatar for any email.
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Check if the URL is cached or not by Google.
Make sure your passwords are good enough.