Take an IP and try to look for the domain/host associated with it.
Get approximate IP details.
Get all possible details about an SSL certificate.
Get all possible details about a domain name.
Ping a website, server or port..
Find A, AAAA, CNAME, MX, NS, TXT, SOA DNS records of a host.
Check if the URL is cached or not by Google.
Get all the HTTP headers that an URL returns for a typical GET request.