Minify your HTML by removing all the unnecessary characters.
Minify your JS by removing all the unnecessary characters.
Get approximate IP details.
Ping a website, server or port..
Get all possible details about an SSL certificate.
Extract email addresses from any kind of text content.
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.