Convert text to binary and the other way for any string input.
Convert text to ascii and the other way for any string input.
Convert text to decimal and the other way for any string input.
Convert text to octal and the other way for any string input.
Get the gravatar.com globally recognized avatar for any email.
Check if the URL is cached or not by Google.
Take an IP and try to look for the domain/host associated with it.
Get all possible details about an SSL certificate.
Get & verify the meta tags of any website.
Make sure your passwords are good enough.