Minify your CSS 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 possible details about an SSL certificate.
Get all the HTTP headers that an URL returns for a typical GET request.
Ping a website, server or port..