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 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.
Extract email addresses from any kind of text content.
Check if the URL is banned and marked as safe/unsafe by Google.
Check for 301 & 302 redirects of a specific URL. It will check for up to 10 redirects.
Check if the URL is cached or not by Google.
Make sure your passwords are good enough.