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