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