Minify your HTML by removing all the unnecessary characters.
Minify your JS by removing all the unnecessary characters.
Get approximate IP details.
Take an IP and try to look for the domain/host associated with it.
Find A, AAAA, CNAME, MX, NS, TXT, SOA DNS records of a host.
Get all the HTTP headers that an URL returns for a typical GET request.
Get all possible details about an SSL certificate.
Ping a website, server or port..