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.
Ping a website, server or port..
Get all possible details about a domain name.
Make sure your passwords are good enough.
Find A, AAAA, CNAME, MX, NS, TXT, SOA DNS records of a host.
Take an IP and try to look for the domain/host associated with it.