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..
Get the gravatar.com globally recognized avatar for any email.
Get & verify the meta tags of any website.
Make sure your passwords are good enough.
Check if the URL is cached or not by Google.
Get details of any file type, such as the mime type or last edit date.
Check for 301 & 302 redirects of a specific URL. It will check for up to 10 redirects.