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.
Get the gravatar.com globally recognized avatar for any email.
Make sure your passwords are good enough.
Find A, AAAA, CNAME, MX, NS, TXT, SOA DNS records of a host.
Check if the URL is banned and marked as safe/unsafe by Google.
Get details of any file type, such as the mime type or last edit date.
Take an IP and try to look for the domain/host associated with it.