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 decimal and the other way for any string input.
Upload a QR code image and extract the data out of it.
Check whether a website is using the new HTTP/2 protocol or not.
Find A, AAAA, CNAME, MX, NS, TXT, SOA DNS records of a host.
Generate a SHA-512 hash for any string input.
Take an IP and try to look for the domain/host associated with it.
Make sure your passwords are good enough.