Take an IP and try to look for the domain/host associated with it.
Get approximate IP details.
Get all possible details about an SSL certificate.
Get all possible details about a domain name.
Ping a website, server or port..
Extract email addresses from any kind of text content.
Get the gravatar.com globally recognized avatar for any email.
Find A, AAAA, CNAME, MX, NS, TXT, SOA DNS records of a host.
Make sure your passwords are good enough.
Check if the URL is banned and marked as safe/unsafe by Google.