Convert text to binary and the other way for any string input.
Convert text to hexadecimal and the other way for any string input.
Convert text to ascii and the other way for any string input.
Convert text to octal and the other way for any string input.
Find A, AAAA, CNAME, MX, NS, TXT, SOA DNS records of a host.
Get the web-host of a given website.
Make sure your passwords are good enough.
Get & verify the meta tags of any website.
Check if the URL is cached or not by Google.
Extract email addresses from any kind of text content.